nervous system

types of neurons

sensory neurons- carry nerve impulses to the brain and spinal chord
motor neurons- carry nerve impulses to the various organs from the CNS
inter neurons- connect motor and sensory neurons

structure of a neuron

axon is a single long process which can conduct nerve impulses. they are covered with a myelin sheath which increases the speed of conduction & insulates the neurons.

between the segments of the axon there are unmyelinated segments called the nodes of ranvier.

between each neuron there is a synapse, which connects the two. at that point the electric singals transform into chemical stimulaiton which stimulate the electric impulse in the next neuron

components of the nervous system

central nervous system	peripheral nervous system	autonomic nervous system
consists of the brain and the spinal chord	its main function is to carry impulses to and from the CNS	pair of muscles close to the organ they need to stimulate
the brain is further divided into the cerebrum, cerebellum and the medula oblongata	it is further divided into the cranial and spinal nerves	divided into the sympathetic and parasympathetic nervous system

sympathetic v parasympathetic

conditioned v unconditioned reflexes

sympathetic NS	parasympathetic NS
fight or flight	rest and digest
arise from the neuron of the thorasic and lumber segments of spinal chord	arise from segments of spinal chord above the neck
helps body adjust to abnormal surroundings	helps body return to normal conditions
heart beat increases, pupils dialate, adrenaline increases	heart beat decreases, pupils constrict.

unconditioned	conditioned
simple reflex	learned response
swallowing, blushing, blinking, breathing	knitting while watching tv

the brain

protected by the cranial bones known as meninges
the meninges (continuouse with the spinal chord) are divided into the dura, arachnoid and pia mater.
the cerebrospinal fluid serves as a shock absorbing medium and protects the rest of the CNS from jerks (located in verticles and cavities ****of the brain)

parts of the brain

forebrain

cerebrum - controls conciousness, memory & reason

composed of outer grey mater & inner white mater
corpus callosum- which is a longitudinal fissure dividing the cerebrum into two halves.

thalamus- centre for interpretation of sensory impulses

locates above the mid brain

hypothalamus - controls body temperature, regulates pituitary gland

small portion below the thalamus

hind brain

cerebellum - maintains body balance, coordinates muslces

pons varoli - connecting two lobes of the cerebellum

ensures coordination of muscular movements on both sides of the cerebellum

medulla oblongata - controls involintary actions

spinal chord

hole in the spinal chord contains the cerbrospinal fluid

reflex arc & action

reflex action*-* quick involunagtry response to a stimulus.

reflex arc*-* the shortest route that can be taken by an impulse from a receptor to an effector

eyes 👁

external structure

eyebrows (junction of the upper eyelid and forehead)- protect the eyes from the rays of the sun

eyelids - shade the eye during sleep

eyelashes (line the eyelids)

lacrimal glands (located at the upper, outer end of the eyeball beneath the eyelid) - manufacture tears

tears- destroy germs and wash the eye surface

internal structure

sclera- tough white protective layer

cornea (transparent continuation of the sclera) - refraction

conjunctiva (anterior to surface of sclera)- protects surface of the eye

choroid (inner to the sclera) - nourishes the eye, absorbs light rays

ciliary body (behind the junction of sclera) - secrete aqueous humor, alters shape for vision

iris (suspended b/w cornea and lens) - regulates amt of light entering the eye

retina (innermost layer) - assure night vision, provide screen for image formation

optic nerve - carry impulses from rods and cones to the brain

colour of vision

the retina has three types of light senstive compounds corresponding to green, red and blue. each cone produces a stimulation in the cerebrum to see the coulour

persistance of vision

the impression of an image remains on the retina for 0.1 seconds. the principal underlying motion pictures is shot at the speed of 24 frames per second.