Nervous System WACE

What is the function of the Nervous System?

The nervous system is the body’s communication network and control centre, maintaining homeostasis by detecting, processing, and responding to changes in the internal and external environment

What are the two main divisions of the Nervous System?

The Central Nervous System (CNS) — composed of the brain and spinal cord, and the Peripheral Nervous System (PNS) — composed of nerves that connect the CNS to receptors, muscles, and glands

What are neurons?

Neurons are specialised nerve cells that transmit electrochemical impulses rapidly throughout the body

What are dendrites and their function?

Dendrites are extensions of a neuron that receive nerve impulses and carry them toward the cell body

What is the function of the axon?

The axon carries nerve impulses away from the cell body towards effectors or other neurons

What is the myelin sheath and its function?

The myelin sheath is a fatty insulating layer produced by Schwann cells that increases the speed of impulse conduction (saltatory conduction), provides protection, and prevents ion leakage

What is white matter and grey matter?

White matter consists of myelinated nerve fibres, while grey matter contains unmyelinated fibres, cell bodies, and synapses

What are Nodes of Ranvier?

Nodes of Ranvier are small gaps in the myelin sheath where ion exchange occurs, allowing saltatory conduction — impulses “jump” between nodes, increasing speed

What is the neurilemma and its purpose?

The neurilemma is the outer layer of the Schwann cell that assists in the repair and regeneration of damaged nerve fibres

What are the three functional types of neurons?

Sensory neurons (afferent) carry impulses to the CNS

motor neurons (efferent) carry impulses from the CNS to effectors

interneurons connect neurons within the CNS

What are the three structural types of neurons?

Multipolar (one axon, many dendrites), bipolar (one axon, one dendrite), and unipolar (one axon only)

What is a nerve impulse?

A nerve impulse is an electrochemical change that travels along a neuron, caused by ion movement across the axon membrane

What is resting membrane potential (RMP)?

The RMP is the difference in electrical charge across a resting neuron’s membrane (approximately –70 mV) due to unequal ion distribution — more Na⁺ outside and more K⁺ inside

Why is the resting membrane polarised?

Because potassium ions (K⁺) diffuse out faster than sodium ions (Na⁺) diffuse in, leaving the inside more negative

What is depolarisation?

Depolarisation occurs when a stimulus (≥15 mV threshold) opens voltage-gated sodium channels, allowing Na⁺ ions to rush in, reversing polarity to +30 mV

What is the “all-or-nothing” principle?

Once the threshold potential is reached, a full action potential occurs — the neuron either fires completely or not at all

What is repolarisation?

After depolarisation, sodium channels close and voltage-gated potassium channels open, allowing K⁺ to diffuse out, restoring the negative charge inside the neuron

What is hyperpolarisation?

K⁺ channels remain open too long, causing the membrane potential to drop below resting potential

How is the resting membrane potential restored?

The sodium–potassium pump (Na⁺/K⁺-ATPase) actively transports 3 Na⁺ out and 2 K⁺ in, restoring ionic balance

What is the refractory period?

The brief period after an action potential during which the neuron cannot be re-stimulated, ensuring one-way transmission of impulses

What are voltage-gated ion channels?

Ion channels that open or close in response to membrane voltage changes, regulating Na⁺, K⁺, and Ca²⁺ flow

What is a synapse?

A junction between neurons (or a neuron and effector) where neurotransmitters transmit impulses across a small synaptic cleft

What are neurotransmitters?

Chemical messengers (e.g. acetylcholine, noradrenaline) that carry signals across the synaptic cleft to receptors on the postsynaptic membrane

Describe transmission across a synapse

Action potential reaches axon terminal → voltage-gated Ca²⁺ channels open → Ca²⁺ influx triggers exocytosis of neurotransmitters → neurotransmitters diffuse across cleft → bind to receptors → new action potential generated

How are neurotransmitters removed from the synaptic cleft?

By reuptake into the presynaptic neuron, enzymatic degradation, or diffusion away from the synapse

What is the difference between unmyelinated and myelinated conduction?

Unmyelinated fibres conduct impulses continuously along the membrane

myelinated fibres conduct impulses via saltatory conduction, jumping between Nodes of Ranvier, which is faster

What is the effect of chemicals on transmission?

Stimulants (e.g. caffeine) increase synaptic transmission

depressants (e.g. anaesthetics) inhibit or block it

What protects the Central Nervous System (CNS)?

Bone (cranium & vertebral canal), meninges (dura mater, arachnoid mater, pia mater), and cerebrospinal fluid (CSF)

What are the meninges and their layers?

Dura mater (tough, outer fibrous layer), arachnoid mater (middle, loose mesh), and pia mater (delicate, vascular inner layer)

What are the functions of cerebrospinal fluid (CSF)?

Protection (shock absorber), transport (nutrients and wastes), and support (buoyancy for the brain)

What is the Autonomic Nervous System (ANS)?

The ANS controls involuntary functions (heart rate, blood pressure, digestion, etc.) and is regulated by the hypothalamus and medulla oblongata

What are the two divisions of the ANS and their functions?

Sympathetic division (“fight or flight”) prepares for stress — increases heart rate, dilates pupils

parasympathetic division (“rest and digest”) conserves energy — slows heart rate, stimulates digestion

What are the neurotransmitters of the ANS?

Sympathetic = noradrenaline (norepinephrine)

Parasympathetic = acetylcholine

How does the ANS differ from the Somatic Nervous System (SNS)?

SNS controls voluntary skeletal muscle using acetylcholine, while ANS controls involuntary organs using acetylcholine or noradrenaline

Compare the structure of ANS and SNS pathways

SNS has one motor neuron to effectors

ANS has two neurons (preganglionic and postganglionic) with a ganglion between

What happens during the fight or flight response?

Sympathetic activation triggers adrenaline/noradrenaline release → increased heart rate, respiration, blood glucose, and blood flow to muscles

What happens during parasympathetic dominance?

The body returns to resting state — heart rate slows, pupils constrict, digestion and gland secretion resume

What are the main structures of the brain?

Cerebrum, cerebellum, hypothalamus, medulla oblongata, and spinal cord

What are the features of the cerebrum?

Outer grey matter (cerebral cortex), inner white matter, and basal ganglia of grey matter

cortex folded into convolutions separated by sulci and fissures

cortex folded into convolutions separated by sulci and fissures

What are the functions of the cerebrum?

Thinking, reasoning, learning, memory, voluntary movement, and sensory perception

What are the three types of tracts in the cerebrum?

Association tracts (within hemisphere), commissural tracts (between hemispheres via corpus callosum), and projection tracts (connect cortex to other brain areas or spinal cord)

What is the function of the cerebellum?

Maintains posture, balance, and fine coordination of voluntary movements through sensory feedback from inner ear and stretch receptors

What is the function of the hypothalamus?

Regulates homeostasis (body temperature, water balance, food intake, sleep, emotional responses), and controls the endocrine system via the pituitary gland

What is the function of the medulla oblongata?

Contains cardiac, respiratory, and vasomotor centres, controlling heart rate, breathing, and blood vessel diameter

What is the spinal cord and its functions?

A cylindrical structure of grey and white matter that transmits sensory and motor impulses between the brain and body and coordinates reflexes

What is a reflex?

A rapid, automatic, stereotyped response to a stimulus that protects the body from harm

What are the characteristics of reflexes?

Require a stimulus, are involuntary, rapid, and stereotyped (same each time)

What are the five components of a reflex arc?

Receptor → Sensory neuron → Interneuron → Motor neuron → Effector

What are receptors and their roles?

Receptors detect changes (stimuli) in the body’s internal or external environment and initiate impulses in sensory neurons

Compare voluntary and reflex actions

Voluntary actions are conscious, slower, and involve cerebral cortex reflex actions are automatic, fast, and involve spinal cord or brainstem

Compare nervous and endocrine control systems

Nervous = rapid, short-lived, electrochemical signals via neurons Endocrine = slower, long-lasting, chemical hormones via bloodstream

List similarities between the nervous and endocrine systems

Both involved in communication, homeostasis, and regulation, both may use similar chemicals (e.g. noradrenaline, adrenaline), some neurons secrete hormones (e.g. oxytocin, ADH)

Steps of reflex

Reflex action (so only involves the spinal cord)

Impulse travels from receptor to spinal cord via a sensory/afferent neuron through the dorsal root

Synapse between a sensory/afferent neuron and an interneuron

In the grey matter of the spinal cord

Synapse between interneuron and motor/efferent neuron

Impulse sent to effector through ventral root Motor/efferent neuron stimulates muscle movement via a neuromuscular junction/across a motor end plate