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
a wave of irritability 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
define meninges
the brain is protected by 3 membranous coverings called meninges which continue backward into the spinal cord
3 layers of meninges
- dura mater (outermost, tough, fibrous)
- Arachnoid (thin delicate middle, web-like cushion)
- pia mater (innermost, highly vascular, rich in blood
function of cerebrospinal fluid
protects the brain from shocks
gray matter
made of cell bodies
brain- outer cortex
spinal cord- inner side
white matter
axons
brain- inner part
spinal cord- outer part
define corpus callosum
sheet of fibres connecting the two cerebral hemispheres and helps to transfer information from one hemisphere to the other
function of cerebrum
seat of intelligence, consciousness, and will-power. controls all voluntary activities
location of cerebellum
at the base and under the cerebrum
function of cerebellum
maintain balance of body and coordinate muscular activity
location of medulla
base of the skull, lowest portion of the brain. continues behind as the spinal cord
function of medulla
controls activity of internal organs, involuntary actions
thalamus
relays pain and pressure impulses to cerebellum
hypothalamus
controls body temperature and pituitary
location of pons
base of the brain just above medulla oblongata
function of pons
carries impulses from one hemisphere of the cerebellum to the other hemisphere and coordinates muscular movements on both sides
location of spinal cord
medulla to the second lumbar vertebrae, lies within neural canal of vertebrae
functions of spinal cord
- reflexes below the neck
- conducts sensory impulses from the skin and muscles to the brain
- conducts motor responses from the brain to the muscles of trunk and limbs
sets of nerves in somatic nervous system
- cranial nerves
- spinal nerves
distribution of spinal nerves
8 in neck region
12 in thorax
5 in lumbar region
5 in sacral
1 in coccygeal
structure of spinal nerve
at the junction of the dorsal and ventral root, sensory and motor fibres separate from spinal nerve. sensory fibre continues in the dorsal root and motor into the ventral root
parts of autonomic nervous system
- sympathetic
- parasympathetic
origin of sympathetic system
arise from spinal cord between the neck and waist region
location of parasympathetic
- anteriorly in the head and neck
- posteriorly in sacral region
sympathetic and parasympathetic system
sympathetic system prepares the body for violent action against abnormal conditions
the parasympathetic system re-establishes normal conditions
define reflex action
automatic/quick involuntary action in the body brought about by a stimulus
types of reflexes
- natural/inborn
- conditioned/ acquired
natural reflex
no previous experience or learning is required. they are inherited from parents
ex: blinking, coughing, sneezing, salivation, peristalisis
conditioned reflex
an involuntary, spontaneous, automatic response brought about due to a previously learned experience
ex: watering of mouth
define reflex arc
the shortest route that can be taken by an impulse from a receptor to effector
define sensory neuron
the neuron in the spinal cord which receives impulses through its axon terminals which are in contact with a receptor cell
define CNS
a region in the spinal cord and brain where incoming sensory impulse generates an outgoing motor impulse
define motor neuron
carries impulse generated by the association neuron in CNS to the effector organ
define effector
an organ that responds to a motor nerve impulse
