Nervous System

What are the two main divisions of the nervous system? And what do they do?

→ CNS (Central Nervous System) : brain and spinal cord.
→ PNS ( Periodic Nervous Systems): cranial and spinal nerves.

PNS contains sensory and motor fibres and connects CNS to muscles, glands and all sensory receptors.

What are the three layers of the meninges, and what else protects the brain?

→ Dura mater, arachnoid mater and pia mater.
→ The brain is also protected by cerebrospinal fluid (CSF).

How are nerve cell bodies and axons organised in the CNS?

Nerve cell bodies are organised into functional clusters called nuclei

while axons are grouped into tracts.

Ganglia, Cranial nerves and spinal nerves

Cranial nerves:

12 pairs emerge from the base of the brain through foramina of the skull.

Spinal nerves:

31 pairs emerge from the spinal cord, each serving a specific part of the body.

Ganglia:

small masses of nervous tissue containing primarily neuronal cell bodies.

What are the three main functions of the nervous system?

Sensory, integrative and motor functions

Sensory Function:

To sense changes in the internal and external environment through sensory receptors.
Sensory (afferent) neurons transport sensory information from the periphery to the CNS.

Integrated functions:

To analyse sensory information, store some of it, and make decisions regarding appropriate behaviours.

Performed by association neurons/interneurons, which connect sensory neurons to motor neurons.

Motor function:

To respond to stimuli by initiating action.
Motor (efferent) neurons send nerve impulses to muscles and glands.

What is the difference between white matter and grey matter?

→ White matter: myelinated processes - white iN color
→ Grey matter: nerve cell bodies, dendrites, axon terminals, unmyelinated axons and neuroglia.

What are the three broad regions of the brain?

Hindbrain, midbrain and forebrain.

→ Hindbrain: cerebellum, medulla and pons.
→ Midbrain: midbrain region.
→ Forebrain: 2 cerebral hemispheres (covered by cerebral cortex) and diencephalon (central mass of grey matter)

What structures make up the brain stem?

The midbrain and hindbrain, with the exception of the cerebellum.

What are neocortex, gyri and sulci?

Neocortex:

A six-layered structure on the surface of the cerebral hemispheres. The layers are numbered I–VI.

Gyri:

ridges on the surface of the cerebral hemispheres.

Sulci:

grooves on the surface of the cerebral hemispheres.

What are the 6 main regions of the CNS

Spinal cord

medulla oblongata

pons

cerebellum

midbrain

diencephalon

cerebral hemispheres,

What is the spinal cord and where is it located?

Controls the movements of the limbs and body and receives and processes sensory information from the body.

A long tubular bundle of nerve cells and supporting cells that extends from the medulla oblongata and is protected by the vertebral column.

What are the functions of main regions of CNS

Spinal Cord: (already mentioned)

Medulla oblongata: Contains centres that control vital autonomic (involuntary) functions, including digestion, breathing and heart rate.

Pons: acts as a relay station conveying information from the cerebral hemispheres to the cerebellum.

Cerebellum: involved in the modulation of movement and learning of motor skills.

Midbrain: controls sensory and motor functions including eye movement and coordination of audio-visual reflexes.

Diencephalon: contains the thalamus and hypothalamus. The thalamus processes most information reaching the cerebral cortex, while the hypothalamus regulates autonomic, endocrine and visceral functions.

Structure within Cerebral Hemispheres:

→ Hippocampus: memory storage.
→ Basal ganglia: regulation of motor performance.
→ Amygdaloid nucleus: coordinates autonomic and endocrine responses with emotional states.

What are the functions of main regions of CNS

Spinal Cord: (already mentioned)

Medulla oblongata: Contains centres that control vital autonomic (involuntary) functions, including digestion, breathing and heart rate.

Pons: acts as a relay station conveying information from the cerebral hemispheres to the cerebellum.

Cerebellum: involved in the modulation of movement and learning of motor skills.

Midbrain: controls sensory and motor functions including eye movement and coordination of audio-visual reflexes.

Diencephalon: contains the thalamus and hypothalamus. The thalamus processes most information reaching the cerebral cortex, while the hypothalamus regulates autonomic, endocrine and visceral functions.

Structure within Cerebral Hemispheres:

→ Hippocampus: memory storage.
→ Basal ganglia: regulation of motor performance.
→ Amygdaloid nucleus: coordinates autonomic and endocrine responses with emotional states.

What are the four regions of the spinal cord?

Cervical

thoracic

lumbar

sacral

What are the principal functions of the spinal cord?

1) Acts as a conduit for motor and sensory information

2) centre for coordinating reflex actions.

What is the organisation of grey and white matter in the spinal cord?

Central grey matter containing neuronal cell bodies is surrounded by white matter containing ascending and descending tracts.

What are the functions of the dorsal and ventral horns?

→ Dorsal horn: receives sensory input.
→ Ventral horn: projects motor output.

Does the spinal cord extend the full length of the vertebral column?

It does not extend the full length and terminates in fibrous extensions known as the filum terminale.

What is the main function of the autonomic nervous system (ANS)?

Maintains homeostasis in an ever-changing environment.

It regulates internal organs and involuntary actions such as breathing and heart rate, functioning at the subconscious level.

It is part CNS and PNS

What are the three subdivisions of the autonomic nervous system?

Sympathetic nervous system

parasympathetic nervous system

enteric nervous system

What are the functions of sympathetic, parasympathetic and enteric nervous systems?

Sympathetic Nervous System:

Controls temperature, respiration, digestion and blood flow in response to demand and mediates the “fight or flight” response.

Parasympathetic nervous system:

“Rest and digest” — conservation of energy, including replenishment and storage, and maintenance of organs during periods of minimal activity.

Enteric nervous systems:

Comprises the intrinsic nerve plexuses of the gastrointestinal tract, closely interconnected with the sympathetic and parasympathetic systems.

What are the two main neurotransmitters that operate in the ANS?

Acetylcholine and Norepinephrine

What is the somatic nervous system (SoNS)?

The part of the PNS associated with voluntary control of movement.

It also communicates information from outside the body through afferent (sensory) and efferent (motor) nerves.

What are the three parts of the somatic nervous system?

→ Spinal nerves: carry information from the external body to the spinal cord and motor information from the spinal cord to muscles.

→ Cranial nerves: carry information into and out of the brainstem.

→ Association nerves: thousands of nerves integrating sensory and motor output.

What is sensation?What are the two major components of the somatic sensory system?

The ability to encode and perceive information generated by stimuli arising from both external and internal environments.

1. A system for detecting mechanical stimuli and temperature.
2. A system for detecting noxious stimuli (nociceptors).

Mechanical stimuli (Light touch, vibration, pressure, cutaneous tension and temperature)

Why is pain essential?What are the three types of pain?

Pain acts as a warning signal of a problem or injury and encourages us to protect the painful area, promoting healing.

→ Nociceptive pain: direct response to tissue damage, inflammation or cancer.
→ Neuropathic pain: not directly linked to tissue damage and can arise from nerve/brain injury or independently.
→ Referred pain: originates from a visceral organ but is perceived in a different area of the body.

What is an example of referred pain and why does it occur?

• Pain during a heart attack felt in the arm.

• It occurs because the body surface is innervated by the same spinal segments as the visceral organ.

What are nociceptors? What are the two main types of nociceptive fibres and what type of pain do they produce?

Sensory (afferent) nerve fibres capable of detecting noxious stimuli.

→ Aδ fibres: thinly myelinated, fast-conducting → sharp, short-term, well-localised pain.
→ C fibres: unmyelinated, slow-conducting → dull, persistent, poorly localised pain.

Which neurotransmitters are released by first-order nociceptive afferent neurons?

Glutamate for fast responses and substance P for slow responses in the ascending pathway

What are the three orders of neurons involved in the sensory pathway?

→ First-order neuron: delivers sensation to the CNS; cell body is in a spinal or cranial nerve ganglion.
→ Second-order neuron: located in the spinal cord or brainstem and passes the signal to the thalamus.
→ Third-order neuron: located in the thalamus and passes the signal to the primary somatosensory cortex.

What is decussation in the sensory pathway?

The process where the axon of the second-order neuron crosses over to the opposite side of the CNS.

Which side of the brain receives sensory information from each side of the body? What are the three major ascending somatic sensory pathways?

→ Right cerebral hemisphere → left side of the body.
→ Left cerebral hemisphere → right side of the body.

• Spinothalamic pathway, posterior column pathway and spinocerebellar pathway.

What is the role of descending pathways in pain?

Why are descending pain pathways important pharmacologically?

• They control impulse transmission in the dorsal horn and can inhibit nociceptive transmission.

• The descending inhibitory pathways are an important site of action for opioid analgesics. A noradrenergic pathway from the locus coeruleus also inhibits transmission in the dorsal horn and may be involved in the action of tricyclic antidepressants for pain.

What is the role of the periaqueductal gray (PAG) in pain control?

Where does the PAG project in the descending pain pathway?

• The PAG, located in the midbrain, is a major pathway through which cortical and other inputs control the nociceptive “gate” in the dorsal horn.

• → PAG → rostroventral medulla (RVM) → spinal cord → dorsal horn.

What areas of the brain are involved in the regulation and integration of movement?

The origin of nerve signals within the somatic nervous system (SoNS) is the motor neurons located in the primary motor cortex in the brain.

a number of brain regions are required for the integration of movement. These include:

• Primary motor cortex

• Supplementary motor area

• Primary somatosensory cortex

• Superior parietal lobe

What is the corticospinal tract and what is its role in movement?

• Nerve fibres originating from the areas involved in movement contribute to the corticospinal tract.

• It is the primary efferent pathway from the cerebral cortex to the spinal cord.

• In addition to the corticospinal tract, other indirect pathways also contribute to motor function.

What is the basal ganglia and which nuclei are involved? What is the function of the basal ganglia in motor control?

It is a collection of deep nuclei within the cerebral hemispheres that impacts on motor control.

The nuclei involved include the:

• Caudate nucleus

• Globus pallidus

• Putamen

• Striatum

It is involved in the modulation of cortical output.

achieved through a feedback circuit linking the cerebral cortex to the basal ganglia.

what is cerebellum it primarily concerned with?

What are the functions of the cerebellum in motor control?

• with the control and coordination of movement,

• acting as a movement control centre by comparing intended movement with actual movement.

• also responsible for “motor memory.”

The cerebellum is involved in:

• Balance

• Maintaining muscle tone

• Gross and fine motor coordination

• Comparing actual movement with intended movement

• Automatically making necessary adjustments to produce smooth and coordinated movement
  It can also “learn” highly specialised motor functions through specific repeated comparator activities.

How do the cortex, basal ganglia and cerebellum work together in motor control?

• The highest level of motor control comes from the cortex,

• while the basal ganglia and cerebellum provide feedback to the cerebral cortex and brainstem.

• The cerebellum has extensive connections with the cerebral hemispheres and spinal cord and contains more neurons than the cerebral hemispheres combined.

What are higher functions of the brain?

→ Higher functions refer to the highest level of control in the hierarchy of the nervous system and constitute all conscious mental activity, including thinking, remembering and reasoning, as well as complex behaviour such as speaking and purposive movement.
→ They also refer to information processing in the cerebral cortex, which predominantly takes place unconsciously.

How is our understanding of higher cortical functions developed, and what disorders can occur when these areas are damaged?

• The anatomy of higher cortical functions is poorly understood.

• Much of what we know has been elucidated through studying individuals with lesions, such as those caused by stroke.
  → Damage can give rise to disorders of:

• Recognition → agnosia

• Language → aphasia

• Complex movement → apraxia

Where is the limbic system located and what structures does it include?

The limbic system lies underneath the cerebral cortex and includes important structures such as the:

• Hippocampus

• Amygdala

• Olfactory lobe

• Habenular nucleus

• Thalamus

What are the functions of the limbic system?

• Limbic structures generate emotional states such as fear, arousal, rage and happiness and contribute to memory processes.

• They also include hypothalamic centres responsible for mediating limbic-generated emotional events and allow reflex movements associated with eating, such as swallowing and chewing.

What is the reticular activating system (RAS) and where is it located?

• The reticular formation is located in the midbrain

• is a network of interconnected nuclei that includes the reticular activating system (RAS).

What is the function of the reticular activating system?

• involved in many involuntary functions.

• Its output directly affects the activity of the cerebral cortex, controlling awareness, attention and wakefulness, and therefore sleep and unconsciousness.