Chapter 9 (part 2)

Neurotransmitters are chemical signals that transmit messages between neurons, influencing various functions such as mood, perception, and motor control.

An action potential (AP) is an electrical signal that travels down the axon of a neuron, allowing for the rapid transmission of information across the nervous system.

The limbic system is primarily involved in deep-seated instincts during stress or crisis, often referred to as the 'Primitive Brain'.

The Limbic System controls emotions, short-term memory, and instinctive behavior.

The Limbic System consists of the following components:

1. Hippocampus
2. Amygdala
3. Thalamus
4. Hypothalamus

The key components of the limbic system involved in learning and emotion include the Hippocampus, Amygdala, and Hypothalamus.

Action potentials are propagated from the axon hillock to the axon terminals through local current flow that depolarizes adjacent inactive areas from resting potential to threshold potential. This activation allows for action potential propagation, while the previous active zone returns to resting potential, entering the refractory period where channel proteins cannot be activated immediately, ensuring unidirectional propagation of the action potential.

The soma end of the axon becomes depolarized in response to a signal.

After depolarization spreads down the axon, the first part of the membrane repolarizes. This occurs because Na+ channels are inactivated and additional K+ channels have opened, preventing further depolarization.

The action potential travels down the axon as the depolarization spreads, while the previous sections of the membrane are repolarizing, ensuring that the action potential continues to propagate in one direction.

A synapse is a junction where a presynaptic neuron releases neurotransmitters to relay signal transmission between neurons.

Examples of neurotransmitters include:

1. Dopamine - found in the CNS
2. Acetylcholine - found in both CNS and PNS
3. Norepinephrine (Noradrenaline) - found in both CNS and PNS

The main components of the Central Nervous System (CNS) are the brain and the spinal cord.

The Central Nervous System (CNS) consists of the brain and spinal cord, while the Peripheral Nervous System (PNS) includes all the nerves that extend throughout the body, connecting the CNS to limbs and organs.

The central nervous system (CNS) consists of the brain and spinal cord.

The motor division of the PNS carries motor commands from the CNS to peripheral tissues and systems.

The sensory division of the PNS brings information to the CNS from receptors in peripheral tissues and organs.

The somatic nervous system (SNS) controls skeletal muscle contractions.

The autonomic nervous system (ANS) provides automatic regulation of smooth muscle, cardiac muscle, glands, and adipose tissue.

Somatic sensory receptors provide sensations of position, touch, pressure, pain, and temperature.

Special sensory receptors provide sensations of smell, taste, vision, balance, and hearing.

Visceral sensory receptors monitor internal organs.

Effectors are target organs whose activities change in response to neural commands.

The Central Nervous System (CNS) is responsible for:

1. Consciousness - allowing humans to think and learn.
2. Voluntary Movement - controlling most voluntary (conscious) movements.
3. Regulation of Non-Conscious Processes - managing processes that occur without conscious thought.

The cerebrum and cerebral cortex are responsible for processing information and determining appropriate actions, which includes various cognitive functions and facilitating conscious experiences.

The limbic system, located in the diencephalon, is primarily involved in managing emotions and short-term memories.

The cerebellum receives information from the brain to regulate body movement and is essential for maintaining body balance.

The cerebrum consists of two hemispheres, which are separated by a deep longitudinal fissure.

The corpus callosum is a large bundle of over 200 million myelinated nerve fibers that connects the two brain hemispheres, permitting communication between them.

The forebrain is primarily composed of the cerebrum and the limbic system.

The outermost layer of the brain is called the cerebral cortex, which is primarily constructed of grey matter containing between 14 and 16 billion neurons.

The cerebral cortex is associated with cognitive functions such as consciousness, thought, reasoning, language, and memory, which contribute to the highest mental capabilities.

Each cerebral hemisphere can be subdivided into four lobes, each associated with different functions.

The frontal lobe is responsible for thinking, planning, and organizing. It also coordinates movement, with the motor cortex initiating skeletal muscle responses.

The parietal lobe functions as a somatosensory cortex for general senses, including pain, temperature, and touch.

The occipital lobe primarily receives signals from the eyes for vision and links and stores information with images related to memory.

The temporal lobe receives signals from the tongue (taste), nose (smell), and cochlea (sound). It is also involved in memory.

Contralateral control refers to the phenomenon where sensory and motor functions from one side of the body are managed by the opposite side of the brain.

The surface area of the somatosensory cortex reflects the number of sensory receptors/neurons in a particular area. A larger surface area for a specific body part indicates greater sensitivity for that part, meaning it can detect sensations more effectively.

The somatosensory cortex is responsible for processing sensory information from the body, including touch, temperature, pain, and proprioception. It interprets signals from the skin, muscles, and joints to create a perception of bodily sensations.

The somatosensory cortex is closely associated with the parietal lobe association area, which integrates sensory information and contributes to spatial awareness and perception. It also interacts with the frontal lobe association area for planning and executing movements based on sensory input.

The somatosensory cortex works in conjunction with other sensory cortices such as the auditory cortex for sound processing and the visual cortex for visual information. This integration allows for a comprehensive understanding of the environment through multiple sensory modalities.

The primary motor cortex is responsible for voluntary muscle contraction and exhibits contralateral control, meaning it controls muscles on the opposite side of the body.

The supplementary motor cortex is involved in the coordination of learned movements, helping to plan and execute complex motor tasks.

Broca's area, located in the premotor cortex, is crucial for controlling speech production and language processing.

The frontal eye field is responsible for the control of voluntary eye movement, allowing for the coordination of eye positioning and tracking.

The primary motor cortex transmits response signals to voluntary skeletal muscles for muscle contraction.

The sensory homunculus represents the relative space that different body parts occupy on the cerebral cortex, with disproportionately large areas for the hands and lips.

The motor homunculus has disproportionately large areas dedicated to the hands, tongue, and mouth, reflecting their importance in motor control.

Wernicke's area is responsible for language comprehension, receiving auditory and visual input to understand language.

Broca's area is involved in language production and instructs the motor cortex to coordinate the delivery of language using the tongue, lips, and vocal cords.

The visual cortex is activated at the back of the brain, processing the visual information of the text being read.

Wernicke's area serves as an association area where the information from the visual cortex is processed and understood before being sent to Broca's area.

Broca's area is involved in the production of speech, receiving processed information from Wernicke's area to formulate the verbal response when reading aloud.

The final step involves the primary motor cortex, which receives information from Broca's area to control the muscles necessary for speech production.

• Able to understand language
• Speech is non-fluent, slow, and consists of incomplete sentences

• Cannot understand language
• Speech is fluent but meaningless

1. Neurons: The basic building blocks of the nervous system that transmit information.

2. Neurotransmitters: Brain chemicals that facilitate communication between neurons.

3. Cerebrovascular system: The network of blood vessels that supply blood to the brain, essential for its function.

Dopamine plays a role in how we feel pleasure, contributes to our ability to think and plan, and helps us strive, focus, and find things interesting.

Serotonin regulates anxiety, happiness, and mood. A lack of serotonin in the brain is associated with depression.

Oxytocin is important in human behaviors including sexual arousal, recognition, trust, anxiety, and mother-infant bonding.

Acetylcholine (Ach) plays an important role in learning and memory.

Endorphins provide pain relief and reduce anxiety. They are present in high concentrations during certain physical activities, such as running.

Glutamate acts as an excitatory neurotransmitter, facilitating communication between neurons.

GABA (gamma-aminobutyric acid) slows down and inhibits nervous activity, contributing to a calming effect.

Sex hormones, produced in the testes and ovaries, are responsible for increasing sexual desire and arousal, contributing to the feeling of lust.

Dopamine, released from the hypothalamus, plays a crucial role in the feeling of attraction by enhancing pleasure and reward, making individuals feel drawn to one another.

Oxytocin and vasopressin, also released from the hypothalamus, are important for forming emotional bonds and attachment between individuals, fostering long-term relationships.

The prefrontal cortex, hypothalamus, and pituitary gland are highlighted, indicating their involvement in the chemical processes related to love, attraction, and emotional bonding.

Serotonin is one of the 'happy' neurotransmitters, and a decrease in serotonin levels is associated with impaired synaptic activity, which can lead to depression.

Dopamine levels are decreased in Parkinson's Disease, contributing to the symptoms of the disorder.

Alzheimer's disease is associated with decreased levels of Acetylcholine, which affects cognitive function.

In depression, there are fewer 'happy' neurotransmitters like serotonin, dopamine, and endorphins, leading to impaired synaptic activity and reduced communication between neurons.

In menopausal women, fluctuating estrogen levels can lead to a drop in serotonin levels, which may contribute to the development of depression.

In Parkinson's disease, there is a reduction in dopamine levels and an increase in the acetylcholine to dopamine ratio, leading to overactivity of acetylcholine.

In a normal brain, dopamine and acetylcholine levels are evenly balanced. In contrast, in Parkinson's disease, dopamine levels are reduced while acetylcholine levels are relatively overactive.

The overactivity of acetylcholine in Parkinson's disease is associated with tremors, which are a common movement-related symptom.

The cerebrovascular system supplies oxygenated blood to the brain and removes metabolic wastes. It is crucial for maintaining neuronal health and function.

During a stroke, if the brain cannot get enough oxygen from the arteries, neurons start to die after a few minutes due to lack of oxygen.

The main arteries involved are:

1. Aorta
2. Brachiocephalic trunk
3. Carotid artery
4. Vertebral artery
5. Basilar artery
6. Cerebral artery

• Sudden weakness
• Paralysis or numbness of the face, arms, or legs (often appearing on one side of the body first)
• Trouble speaking or understanding speech
• Trouble seeing
• Inability to write

The 'F' stands for Face. Check if one side of the face droops by asking the person to smile.

If one arm is weak or numb, ask the person to raise both arms. If one arm drifts downward, it may indicate a stroke.

Ask the person to repeat a simple sentence. If their speech is slurred or the sentence is not repeated correctly, it may indicate a stroke.

If any symptoms of stroke are present, it is crucial to call 999 or get to the hospital immediately, as every minute counts.

An ischemic stroke occurs when an embolus blocks the O₂-rich blood flow to an area of the brain, leading to necrosis and irreversible cell damage due to lack of oxygen.

A hemorrhagic stroke occurs when a cerebral artery is ruptured, causing bleeding and accumulation of blood in the brain, which puts pressure on the brain and leads to a loss of blood to surrounding areas.

The major causes of hemorrhagic stroke include:

1. Hypertension
2. Atherosclerosis

These conditions lead to arteries becoming non-elastic, making them more prone to rupture under high blood pressure.

Hemorrhagic strokes are less common than ischemic strokes, accounting for approximately 15% of all strokes, but they are responsible for about 40% of all stroke deaths.

Mild Traumatic Brain Injury (MTBI), commonly known as a concussion, is a reversible interference with brain function caused by a temporary injury from a mild blow to the brain. It leads to sudden excessive movement of the brain, disrupting neurologic function and causing cellular damage, which may result in loss of consciousness.

The warning signs of a concussion include:

• Headache
• Dizziness
• Nausea/vomiting
• Fatigue
• Vision issues
• Confusion

Individuals may experience symptoms such as confusion, headaches, and memory loss following a TBI. The severity of these effects can vary based on the injury's severity.

The key factors include:

1. Neuroinflammation and cellular damage
2. Cognitive impairment
3. Increased risk of neurodegenerative changes
4. As these changes progress, individuals may meet the clinical criteria for dementia, experiencing significant memory loss and confusion.

Dementia is an overall term for diseases and conditions characterized by a decline in cognitive functions such as memory, language, problem-solving, and other thinking skills. It is often associated with neurodegenerative disorders where damaged neurons in specific regions impair normal function.

MRI (Magnetic Resonance Imaging) is used to check for brain damage.

Functional MRI (fMRI) shows brain activity and blood flow.

An electroencephalogram (EEG) records the electrical potential difference between different points of the brain, reflecting the cerebral cortex activity.

The four basic waveforms in an EEG are:

NREM sleep consists of 4 stages characterized by:

1. Gradual reduction of brainwave frequency.
2. Stage 3 and 4:
   • Known as slow wave sleep/deep sleep.
   • More difficult to awaken from.
   • Dreaming may occur.
   • Possible consolidation of memory.

During REM sleep, the following occurs:

• 3-5 intervals per night.
• Rapid eye movements.
• Low muscle tone.
• Dreaming is prevalent.

The brainwave patterns for different sleep stages are as follows:

• Awake: Alert, beta rhythm
• Drowsy: Alpha rhythm
• NREM Sleep:
  • Stage 1: Theta rhythm
  • Stage 2: Sleep spindles and K complexes
  • Stages 3 and 4: Delta rhythm
• REM Sleep: REM pattern, similar to awake beta rhythm

The characteristics of each sleep stage are:

The limbic system processes emotions first, as indicated by the phrase 'We feel it first...' before the rational brain assigns meaning to those emotions, as shown by the phrase '...then we assign meaning.'

The hippocampus is critical for forming new memories and spatial orientation.

Sustained damage to the hippocampus can lead to progressive neurodegeneration, resulting in dementia.

Alzheimer's disease is the most common cause of dementia, accounting for 60-80% of dementia cases.

Alzheimer's disease leads to irreversible loss of neurons, particularly in the hippocampus, followed by destruction of the cortex and brainstem.

In the early stages, memory loss is mild. In late-stage Alzheimer's, individuals lose the ability to carry on a conversation and respond to their environment.

The two abnormal structures are plaques, which are deposits of beta-amyloid protein fragments that build up between neurons, and tangles, which are twisted fibers of tau protein that build up inside neurons.

On average, a person with Alzheimer's lives 4-8 years after diagnosis.

The thalamus serves as a relay station for sensory and motor pathways, processing and transmitting information to the appropriate areas of the brain.

1. Midbrain
2. Pons
3. Medulla oblongata

The brainstem is responsible for:

• Alertness
• Breathing cycle
• Heart function
• Peripheral resistance in blood vessels

The brainstem has several key functions:

1. Regulates cardiac and respiratory functions
2. Maintains consciousness and the sleep cycle through regulation of the CNS
3. Connects with peripheral nerves:
   • Ascending pathways (sensation):
     • Dorsal column pathway (fine touch, vibration sensation, proprioception)
     • Spinothalamic tract (pain, temperature)
   • Descending pathway (motor function):
     • Corticospinal tract (motor)

The Reticular Activating System (RAS) consists of hyper-excitable neurons that extend from the brainstem to the cerebral cortex. Its primary function is to filter and route incoming sensory information directly to the appropriate location in the brain, thereby helping to focus attention and alertness.

The thalamus acts as a relay station for sensory information, directing it to the appropriate areas of the cerebral cortex for processing. It receives inputs from various sensory modalities, including visual and auditory inputs, and transmits this information to the cortex for interpretation.

The reticular formation contains both ascending sensory fibers, which carry sensory information to the brain, and descending motor fibers, which send signals from the brain to the spinal cord to control motor functions. This interaction is crucial for regulating arousal, attention, and reflexes.

The illustration shows connections for two types of sensory inputs: visual input from the eye and auditory input from the ear. These inputs are linked to the brainstem, which processes and relays this sensory information to higher brain centers.

1. Blood-brain barrier
2. Skull
3. Meninges: 3 protective connective tissue layers
4. Cerebrospinal fluid: located between meninges, absorbs and disperses excessive mechanical force.

The BBB serves as a selective barrier that prevents harmful substances from entering the brain while allowing essential nutrients and oxygen to pass through. It also protects the brain from hormones and acids in the blood and shields it from drastic environmental fluctuations.

The BBB is formed by:

1. Capillary with tight junctions - prevents intercellular clefts for filtration.
2. Astrocytes - glial cells that reduce capillary permeability and transport substances selectively, such as glucose.

The primary function of the blood-brain barrier (BBB) is to protect the brain from potentially harmful substances while allowing essential nutrients, such as glucose and oxygen, to pass through. It regulates the movement of ions, vitamins, and organic nutrients, maintaining a stable environment for the brain.

Factors that can disrupt the blood-brain barrier include:

1. Microwaves
2. Radiation
3. Trauma
4. Hypertension
5. Infection

These factors can lead to increased permeability of the BBB, allowing substances that are normally restricted to enter the brain.

The blood-brain barrier is composed of several key components:

These components work together to regulate the exchange of substances between the blood and the brain.

Cerebrospinal fluid (CSF) serves several key functions in the CNS:

• Acts as a cushion to protect the brain and spinal cord
• Reduces pressure and friction within the CNS
• Removes harmful substances
• Transports chemicals to remote sites inside the CNS

An excess of cerebrospinal fluid (CSF) can lead to a condition known as Hydrocephalus (腦積水).

Cerebrospinal fluid (CSF) samples are analyzed through a procedure known as lumbar puncture or spinal tap.

The total volume of cerebrospinal fluid (CSF) in the human body is approximately 125-150 mL.

The main functions of the spinal cord include:

1. Conduction: Transmits information up and down the body.
2. Reflexes: Facilitates involuntary stereotyped responses.
3. Locomotion: Involves central pattern generators that help in movement coordination.

The spinal cord is protected by:

• Vertebrae (spine)
• Meninges

The spinal cord consists of gray matter and white matter.

The ventral and dorsal roots emerge from their corresponding horns.

The two main divisions of the Peripheral Nervous System are the Afferent division and the Efferent division.

The Afferent division is composed of a Sensory component that is further divided into:

1. Somatic sensory
2. Visceral sensory
3. Special sensory

The Efferent division consists of a Motor component that includes:

1. Somatic motor
2. Autonomic motor (which branches into:
   • Sympathetic
   • Parasympathetic
   • Enteric Digestive system)

The primary function of the Central Nervous System is to process and integrate information from the body and coordinate responses, serving as the control center for the entire nervous system.

The dorsal horn transmits sensory pathways from the dorsal root into the spinal cord, processing afferent sensory information.

The ventral horn extends motor pathways beyond it, sending efferent signals to target organs via the ventral root.

The cell body of the neuron is located at the dorsal root ganglion, which connects to the dorsal horn.

The main components of the somatic sensory pathway include:

1. Sensory neuron in the skin
2. Nerve that transmits signals to the spinal cord
3. Spinal cord segment where the signal is processed
4. Medulla oblongata which relays the signal to the brain
5. Sensory cortex in the brain where the signal is interpreted.

The motor cortex is responsible for:

• Initiating voluntary movements by sending signals to muscle fibers.
• Processing information from the medulla oblongata and spinal cord to coordinate muscle activity.