Chapter 13 - The Nervous System

Neurone

specialised cell that transmits impulses via action potentials

Homeostasis

maintenance of stable equilibrium within the body

Stimulus

detectable change in and organism’s in/external environment

Response

reaction to a stimulus

Neurotransmitters

chemical involved in communication of neurones/muscles across synapse

Dendron

short extensions that carry impulses towards cell body

Axon

short extensions that carry impulses away from the cell body

Myelin sheath

lipid rich membrane surrounding parts of the axon in some neurones

Schwann cell

specialised cells that produce the myelin sheath

Node of Ranvier

unmyelinated part of the axon

Effector

muscle/gland that carries out response

Transducer

an organ that converts stimulus (light/sound/pressure) into electrical impulses

Stretch mediated sodium ion channel

membrane channels in neurones that open when pressure is applied to the Pacinian corpuscle

Na/K pump

membrane protein that maintains normal gradients of Na+ and K+ in neurone

Resting potential

difference in charges across membrane of axon (-65 mV)

Action potential

change in charge over the neurone membrane when stimulated (+40 mV)

Polarised

when there is a slight difference in charge (less positive inside than outside)

Depolarised

change/swap in potential difference

Repolarised

returning to normal polarisation

Voltage-gated sodium ion channels

membrane channels that open as action potential crosses it

Hyperpolarisation

period beyond repolarisation when there’s too much polarisation

Refractory period

period after impulse when axon can’t be excited

Saltatory conduction

the mechanism whereby an impulse ‘jumps’ over a node of Ranvier

Threshold value

the minimum amount of stimulus required to trigger a response

Synapse

junction between neurones or neurone and effector

Synaptic cleft

gap between neurones

Presynaptic neurone

neurone that the impulse comes from

Postsynaptic neurone

neurone that receives neurotransmitter

Synaptic knob

swollen end of neurone

Synaptic vesicles

vesicles containing neurotransmitters

Neurotransmitter receptors

where NTMs bind

Excitatory

NTMs that lead to depolarisation

Inhibitory

NTMs that lead to hyperpolarisation

Summation

build up of NTMs which triggers a response

Spatial summation

NTMs come from lots of different pre-neurones to one post-neurone, building up to threshold, triggering an action potential

Temporal summation

waves of NTMs come from one neurone and builds up to threshold, triggering an action potential

CNS

central nervous system (brain and spinal cord)

PNS

peripheral nervous system (all connecting neurones)

Somatic

conscious/voluntary system of control 

Autonomic

unconscious system that’s constantly working e.g. smooth muscle

Sympathetic

used for fight or flight reactions (noradrenaline)

Parasympathetic

used for relaxation responses (acetylcholine)

Reflex action

involuntary response to a stimulus

Cerebrum

controls voluntary actions

Cerebellum

controls movement, balance and muscle/motor coordination

Medulla oblongata

autonomic control, involuntary actions such as breathing rate

Hypothalamus

regulates temperature and water, maintains homeostasis, produces hormones and stimulates pituitary gland

Pituitary gland

stores and releases hormones

Skeletal muscle

bulk of muscle tissue, responsible for movement

Cardiac muscle

found in the heart, myogenic muscle (provides its own impulses)

Involuntary muscle

involuntary functions (e.g. peristalsis)

Sarcolemma

plasma membrane surrounding bundle of muscle fibres

Sarcoplasm

shared cytoplasm within a muscle fibre

Myofibrils

cylindrical organelles found in muscle used for muscle contraction

Actin

thin protein filament that is slid over myosin in muscle contractions

Myosin

thick protein filament that pulls actin across it in a muscle contraction

Sarcomere

functional unit of myofibril

Sliding filament model

movement of actin filaments over myosin ones causing muscle contractions

Power stroke

the movement of myosin heads pulling actin along

Troponin

small molecule to which Ca2+ binds that moves tropomyosin

Tropomyosin

long molecule that blocks actin binding sites until moved by troponin