Nervous System Flashcards
need for nervous system
- keeps us informed
- remember, think, reason
- controls and harmonises all voluntary muscular activities
- regulates involuntary activites`
what is myelin sheath
axon is covered by a white insulating sheath which is covered by an outermost think layer called neurolemma
what are collaterals
axons may have side branches called collaterals
define synaptic cleft
axon terminals are closely plased near the dendrites of another one or more neurons but are not connected, and gaps are called synaptic clefts
define impulse
electrical impulse that sweeps over a nervous cell
define receptors
the specialised epithelial cells which, on receiving the stimulus, set up waves of impulses towards the central nervous system
define effectors
muscles or glands which, on receiving impulse from brain or spinal cord, contract or secrete substances
polarised state
when outer side of nerve fibre carries positive charge, due to more Na ions outside the axon membrane
depolarised state
when, due to impulse, axon membrane becomes permeable. Na ions move inwards and causes loss of polarisation
repolarised state
previous area of nerve fibre becomes repolarised due to active transport of Na ions again on the outside, using ATP
define synapse
point of contact between the terminal branches of the axon of a neuron with the dendrites of another neuron separated by a fine gap
neurotransmitter
acetylcholine
types of neurons
- sensory (receptor to CNS)
- motor (CNS to effector)
- connecting (connects sensory and motor)
define nerves
nerve is a bundle of nerve fibres (axons) of separate neurons, enclosed in a tubular sheath.
function of myelin sheath in nerves
prevents mixing up of impulses in adjacent axons
kinds of nerves
- sensory
- motor
- mixed
define ganglia
aggregates of the cytons or cell bodies of nerve cells from which the nerve fibres may arise or enter into
subdivisions of PNS
- somatic nervous system
- autonomic nervous system
somatic nervous system
conveys information to voluntary muscles
autonomic nervous system
pair of chains of ganglia and nerves which control the involuntary muscles
weight of brain
1.35 kg