A&P12 U7: Nervous System

A comprehensive set of vocabulary flashcards covering the structure, function and physiology of the nervous system for Biology 12 Unit 7.

Neuron

Specialised nerve cell that conducts electrochemical signals throughout the nervous system.

Central Nervous System (CNS)

Comprises the brain and spinal cord; processes information and issues commands.

Peripheral Nervous System (PNS)

All nerves outside the CNS that connect receptors and effectors to the brain and spinal cord.

Dendrite

Branched fibre that conducts impulses toward a neuron's cell body.

Cell Body (Soma)

Part of a neuron containing the nucleus and organelles; relays impulses from dendrites to the axon.

Axon

Single long fibre that conducts nerve impulses away from the cell body.

Myelin Sheath

Protective, insulating coating formed by Schwann cells around many axons and dendrites.

Schwann Cell

Glial cell of the PNS that wraps its membrane around an axon to form myelin.

Node of Ranvier

Gap between adjacent Schwann cells where the axonal membrane is exposed; speeds conduction.

Saltatory Conduction

Rapid impulse transmission that jumps from node to node along a myelinated fibre (≈ 200 m/s).

Unmyelinated Fibre

Axon lacking a myelin sheath; impulse travels continuously and slowly (≈ 0.5 m/s).

Sensory Neuron

Conducts impulses from receptors to the CNS; afferent pathway.

Interneuron (Relay/Connector)

Neuron within the CNS that transmits impulses between sensory and motor neurons.

Motor Neuron

Carries impulses from the CNS to effectors such as muscles or glands; efferent pathway.

Ganglion

Cluster of neuron cell bodies located outside the CNS.

Action Potential

Brief reversal of membrane polarity (≈ +30 mV) that propagates along an axon during a nerve impulse.

Resting Potential

Stable, negative membrane potential of a non-firing neuron (≈ –70 mV).

Depolarisation

Phase of the action potential when Na⁺ influx makes the inside of the membrane positive.

Repolarisation

Return toward resting potential as K⁺ exits the neuron, restoring negativity inside.

Threshold Potential

Critical membrane voltage that must be reached to trigger an action potential; basis of the all-or-nothing response.

Refractory Period

Short recovery phase following an action potential when a neuron cannot fire again.

Sodium–Potassium Pump

Active transport protein that expels 3 Na⁺ and imports 2 K⁺ to maintain the resting potential.

Voltage-Gated Sodium Channel

Membrane protein that opens when the membrane depolarises, allowing Na⁺ influx.

Voltage-Gated Potassium Channel

Channel that opens later in an action potential, permitting K⁺ efflux for repolarisation.

Stimulus-Response Model

Pathway: receptor → sensory neuron → CNS → motor neuron → effector.

Reflex Arc

Rapid, involuntary pathway that bypasses the brain: receptor → sensory neuron → spinal interneuron → motor neuron → effector.

Synapse

Junction between two neurons (or a neuron and effector) where transmission is chemical.

Neurotransmitter

Chemical messenger released into a synaptic gap to stimulate or inhibit the next cell.

Acetylcholine

Neurotransmitter that generally slows body activity; key in parasympathetic responses.

Noradrenaline (Norepinephrine)

Excitatory neurotransmitter/hormone that speeds body activity; prominent in sympathetic responses.

Synaptic Vesicle

Membrane-bound sac storing neurotransmitter in an axon terminal.

Presynaptic Membrane

Axon-terminal membrane that releases neurotransmitter via exocytosis.

Postsynaptic Membrane

Dendritic or effector membrane containing receptors for neurotransmitter binding.

Ca²⁺ (Calcium Ions)

Enter axon terminal on impulse arrival, enabling vesicle fusion and neurotransmitter release.

Contractile Proteins

Axonal proteins that move synaptic vesicles to the presynaptic membrane when bound to Ca²⁺.

Monoamine Oxidase

Enzyme that breaks down noradrenaline in the synaptic cleft.

Acetylcholinesterase

Enzyme that hydrolyses acetylcholine, terminating its synaptic action.

Afferent Pathway

Route carrying impulses toward the CNS (sensory).

Efferent Pathway

Route carrying impulses away from the CNS to effectors (motor).

Central Canal

Fluid-filled channel running through the spinal cord, containing cerebrospinal fluid.

White Matter

Myelinated interneuron tracts in the CNS.

Gray Matter

Region of neuronal cell bodies within the CNS.

Medulla Oblongata

Brain-stem region controlling vital functions like heartbeat, breathing and blood pressure.

Cerebellum

Hindbrain structure regulating muscle coordination, balance and posture.

Hypothalamus

Brain region linking nervous and endocrine systems; maintains homeostasis.

Thalamus

Relay station directing sensory input to the cerebrum; prevents sensory overload.

Cerebrum

Largest brain part; handles conscious thought, voluntary movement, sensation and memory.

Corpus Callosum

Thick bundle of fibres connecting the left and right cerebral hemispheres.

Somatic Nervous System

PNS division that controls voluntary skeletal-muscle movements and receives external stimuli.

Autonomic Nervous System

PNS division regulating involuntary actions of organs and glands.

Sympathetic Division

Autonomic branch producing the Fight-or-Flight response; uses noradrenaline.

Parasympathetic Division

Autonomic branch promoting Rest-and-Digest functions; uses acetylcholine.

Fight-or-Flight Response

Body-wide sympathetic reaction preparing for immediate action under stress.

Rest-and-Digest

Parasympathetic state that conserves energy and promotes digestion and recovery.