the nervous system Cheat Sheet (DRAFT) by piyamajithia

✓ neurons are excitable cells.
✓ neuroglial cells protect, support and nourish the neurons. (more than one half volume of neural tissue)
✓nissl granules are the granular bodies also present in branched projec­tions of the cell body called dendrites.
✓ dendrites transmit impulses towards cell body
✓distal branched ends of axon are bulb-like structures called synaptic knob. they possess vesicles that release neurot­ran­smi­tters.
✓ axons transmit nerve impulse away from cell body to synapse a neuro-­mus­cular junction.

➤ pons
-consists of fibre tracts that interc­onnect different regions of the brain

➤ cerebellum
-provides additional space for more neurons

➤medulla
-connected to the spinal cord
-centres that control respir­ation, cardio­vas­cular reflex, gastric secretions

➤brain stem
-midbrain, pons, medulla oblongata

➤ 1. outer ear
-pinna and external auditory meatus (canal)
-pinna collects vibrations in the air
-canal has fine hairs and wax-se­creting ceruminous gland
-tympanic membrane composed of connective tissue with skin outsde and mucus membrane inside.

➤2. middle ear
-3 ossicles called malleus, incus, stapes.
-malleus attached to tympanic membrane and stapes to oval window of the cochlea
-eustachian tube connects the middle ear cavity to pharynx
-it helps in equalizing the pressures

➤3. inner ear
-fluid filled ear is called labyrinth which can be divided into bony and membranous
-bony labyrinth is a series of channels inside which lies membranous labyrinth surrounded by perilymph
-membr­anous labyrinth is filled with the fluid endolymph
-coiled portion of the labyrinth is called cochlea
-reissner's and basilar divide the perilymph into upper scala vestibuli and lower scala vestibuli
-space within cochlea is called scala media
-organ of corti is located on the basilar membrane contains hair cells acting as auditory receptors.

✓ inform­ation processing organ- command and control system
✓voluntary and involu­natary movements, balance, thermo­reg­ula­tio­n,h­unger thirst, circadian, endocrine and behaviour.
✓cranial meninges- outer layer dura mater, thin middle layer arachanoid, inner layer in contact with brain tissue pia mater

-located between hypoth­alamus of the forbrain and pons of the hindbrain
-cerebral aqueduct, a canal passes through midbrain
-dorsal portion consists of 4 round lobes called corpora quadri­gemina

- cranial nerves (12 pairs)
- spinal nerves ( 31 pairs)

➤reflex pathway.
-atleast 1 afferent neuron (receptor) and one efferent neuron in series.
-afferent neuron receives signal from sensory organ via dorsal nerve root into CNS
- efferent neurons then carry the signals from CNS to effector and this mechanism is called the reflex arc

-basal end of hair is in close contact with the afferent nerves
-a large no. of processes called stereo cilia are projected from the apical part of ech hair cell.
-thin elastic membrane above hair cells tectorial membrane
-above the cochlea, a complex system called vestibular apparatus
which is composed of 3 semi-c­ircular canals and otolith
-proje­cting ridge containing hair cells crista ampullaris
-saccule and utricle contain a projecting ridge called macula
-crista and macula are specific recept­orsof vestibular apparatus.
mainte­nance of body and posture

✓ ion channels are select­ively permeable

1. resting state
K+ more permeable and Na+, -ve proteins imperm­eable.
axoplasm inside has high conc of K+ and -ve proteins and low conc of Na+.
ECF (extra cellular fluid) has low K+ and -ve proteins but more Na+ therefore forms a concen­tration gradient
ionic gradient maintained by active transport and sodium potassium pup by 3Na+ out 2K+ in.
outer surface = +ve charge inner surface+ -ve charge
polarised state has a potential difference of -70mV
resting potential

2. depola­ris­ation
site permeable to Na+ causing rapid influx therefore reversal of polarity
outer = -ve charge inner= +ve charge
this is now called action potential or nerve impulse

3. repola­ris­ation
Na+ permea­bility was short lived, therefore, followed by a rise in permea­bilty of K+
where K+ diffuses outside restoring the resting potential.

➤ 1. sclera
-dense connective tissue
-anterior portion turns transp­arent and is then called cornea

➤2. choroid
-middle layer, many blood vessels
-thin posterior, anterior thick which forms the ciliary body

➤3. ciliary body
-continues forward to form a pigmented opaque structure iris
-eye call contains transp­arent crysta­lline lens held in place by ligaments

➤4.retina
-3 layer of neural cells ganglion cells, bipolar cells, photor­eceptor cells
-blind spot = no photor­eceptor cells present
-macula lutea- fovea, concen­tration of cones
-space b/w cornea and lens= aqueous chamber containing aqeuous humor
- space b/w lens and retina = vitreous chamber

➤ cerebrum
- 2 halves called the left and right cerebral hemisp­heres
- tract of nerve fibres that connect the hemisp­heres corpus callosum covered with myelin sheath, giving whitish appearance therefore called white matter
-layer that covers cerebral hemisphere and forms prominent folds is cerebral cortex
-cerebral cortex referred to as grey matter due to concen­tration of neurons there.
-contains motor areas, sensory areas, and associ­ation areas (neither motor nor sensory)
-cerebral cortex is respon­sible for inters­ensory associ­ations, memory and commun­ica­tion.

➤ thalamus
-cerebrum wraps around this structure
- major coordi­nating structure for sensory and motor signaling

➤ hypoth­alamus
-lies at the base of thalamus
-body temp, eating, thirst
-groups of neuros­ecr­etory cells secrete hormones called hypoth­alamic hormones

➤limbic system
-inner parts of cerebral hemisp­heres and structures like amygdala, hippoc­ampus, etc
-along with hypoth­alamus involved in rage, pleasure, motiva­tion, sexual behaviour

➤ nose
-contains mucus-­coated receptors called olfactory receptors
-made of olfactory epithelium that consist of 3 kinds of cells
-neurons of olfactory epithelium extend directly in broad bean-sized organs called olfactory bulb this is an extension of the brain's limbic system.

➤ tongue
-detection through tastebuds that contain gustatory receptors

-both nose and tongue detect dissolved chemicals.