User:Tofubird/bio

Nervous System

 * made primarily out of neurons
 * neurons have multiple parts:
 * dendrite
 * nucleus
 * cytoplasm
 * cell memb
 * axon (long tail)
 * axon terminal (has terminal dendrites)
 * cell body (soma)


 * neurons don't have a centriole, so they can't divide when mature
 * some axons are myelinated - wrapped in myelin sheath. the sheath is made from special fatty cells called schawnn cells.


 * the gap between schawnn cells is called the node of Ranvier
 * signals jumping from node to node travel 100s of times fasterthan those just going along the axon due to saltatory conduction
 * therefore, myelinated nuerons faster than unmyelinated

myelin sheath functions

 * provide protection and give nutrition to axon
 * insulate the axon
 * speed up transmission of impulses


 * myelinated is white
 * unmyelinated is grey

three types of neurons

 * sensory
 * motor
 * association

nerves
nerves are bundles of nerv fibres and blood vessels

2 structural types of nerves:
 * spinal - emerges from spinal cord; mixed nerve
 * cranial nerve - emerges from brain; 12 pairs in man

functional types

 * sensory - brings impulses from receptor to CNS
 * motor - brings impulses from CNS to effector
 * mixed - carrying impulses in both directions

the CNS
spinal cord has a central canal (the fluid extends to the ventricles in the brain
 * the canal is filled up with cerebrospinal fluid


 * grey matter is found in the inner H-shaped mass
 * white matter is found around the H-shaped mass

the spinal cordand the brain
 * meninges are three layers of tissues which envelope

reflexes
a reflex is an inborn, rapid, automated stereotyped response not under the conscious control of the brain reflexes are made from an arc of neurons simplest one has two neurons, one sensory and one motor example: knee jerk

conditioned reflex: learned, and therefore coordinated by the brain eg, toilet training

how the nerve impulse works
1. resting potential OUTSIDE: sodium > potassium INSIDE: sodium < potassium NEGATIVELY CHARGED INSIDE, -70 to -90 mV

imbalance maintained by active transport of ions; sodium-potassium pump (pushes in 2 potassium inside while pumping out 3 sodium); potassium channels in membrane are leaky so potassium leaks out slowly

1a. stimulus sodium channels open, sodium rushes in as a result, the cell is depolarized needs to reach threshold for action potential to generate threshold is usually around -50mV

2. Action potential remaining sodium channels open, so thousands of Na+ rush inside the depolarization opens up more and more voltage gated sodium channels (this creates a wave called the nerve impulse)

3. repolarization resting potential is restored again when the permeability is reduced sodium channels have closed potassium channels open sodium ions are pumped out at the end, the potassium channels close again hyperpolarization occurs because the cell has overshot the permeability to potassium than normal

all or nothing law: if it doesn't reach above the threshold, nothin' happens

transmission speed: larger the fibre = less resistance myelination = faster because of saltatory conduction body temperature = warmer is faster because of higher metabolic rate which means faster repolarization and membrane recovery time

the synapse: junction between neurons there are two main transmitter substances: acetylcholine and noraadrenaline

when a nerve impulse is there, it triggers the axon terminal to open calcium-ion-channels. calcium therefore enters the synaptic knob. this then causes vesicles to move towards the presynaptic membrane, and it fuses with the vesicles that are already there. this causes a neurotransmitter to be released into the synaptic cleft. the NT then diffuses across the synaptic cleft. the neurotransmitter attaches to a receptor site on the postsynaptic membrane. when this happens, the sodium ion channels open in the postsynaptic membrane, so it depolarizes. meanwhile, the NT is hydrolized by enzymes; acteycholine turns into choline, and is reabsorbed by the snaptic knob to be recycled back into acetylcholine

common NT's acetylcholine: neuromuscular, excitatory noradrenaline: areas of brain/spinalcord, depends

summation: temporal (two of the same on top of each other) spatial (two different on top of each other) cancellation (inhibitor)

structure of the brain: forebrain, midbrain, hind-brain

forebrain: cerebrum: big part, makes you think. outer layer has a lot of grey matter, inner layer is white. thalamus: relays impulses travelling from other parts of the brain to the cerebrum. pons: connects lower parts of brain to upper parts. hypothalamus: situated below and in front of thalamus, controls ANS pituatary gland: runs the endocrine system

hindbrain: cerebellum: does your balance and fine motor control medulla oblongata: controls involuntary things and reflexes

ANS: parasympathetic and sympathetic ganglion out vs. ganglion in acetylcholine vs. noradrenaline inhibitory vs excitatory boring vs. killer good

--- the senses

---

6 diff kind of receptors: mechano chemo audio photo thermo electro

2 layers of skin epidermis dermis sensory receptors located in dermis.

temperature - free nerve pain - free nerve touch - meissner (touchme) pressure - pacinian (pressure p)

the eye: choroid - supply oxygen + nutrients, remove waste from eye black pigment also reduces internal reflection

cornea - transparent, so light can go in curved surface to refract light and converge it to retina protects front parts of eye

ciliary body: attached to suspensory ligament. regulates the convexity of lens.

iris: contains circular/radial muscles which regulate the size of pupil.

NVCCC: NEAR VISION CIRCULAR CILIARY CONTRACT -> LENS MORE CONVEX

dark conditions: more rhodopsin, so more light sensitive. rhodopsin made from vitamin a

colour: three types of cones, use iodopsin

presbyopia: old flower, lens less elastic, ciliary muscles weak astigmatisM: football eyes

ears: pinna auditory canal tympanum malleus incus stapes/hammer anvil stirrup oval window perilymph; vestibular canal, vestibular membrane basilar membrane, organ of corti, tectorial membrane, endolymph perilymph, tympanic canal round window

ampulla, cupula ,responsible for dynamic equilibrium works by jellymass moving hair cells utriculus sacculus sense gravity/linear acceleration uses otoliths(stones) that are set on top of hairs. if the stones accelerate, the hairs move.

anterior pituatary gland: andrenocorticotrophic hormones -> stimulate production of glucocorticoids growth hormone -> make cells grow prolactine -> make milk gonadotrophic hormones -> LH and FSH. LH stimulates ovulation/secretion of testosterone. FSH stimulates development of gametes and also gonadal hormones. TSH -> stimulates thyroid to make thyroxine

PPG: Oxytoccin-> lets milk go out ADH -> increase reabsorption of water in kidneys

thyroid: thyroxine -> increase metabolism

parathyroid: calcitonin -> reduce blood calcium PTH -> increase blood calcium

pancreas: insulin -> reduce blood glucose glucagon -> increase blood glucose

adrenal gland: adrenaline -> attack noradrenaline -> relax

adrenal cortex: mineralocorticoids (aldosterone) -> maintain electrolyte balance, therefore affecting blood volume (increase in aldy = increase in sodium reabsorption in kidneys, which means more blood volume/pressure_ glucocorticoids -> long term, slow response to stress by raising blood glucose through breaking down fat sex steroids -> testosterone

reproductive system: testes are at 35 degrees so sperm can be made productively each teste contins 1000 seminiferous tubulues seminferous tubules make sperm scrotum: you know what this is epididymis: collects sperm and stores them vas deferens: sperm duct urethra: yep seminal vesicles: glands here produce seminal fluid that contains sugars and proteins prostate gland: contains alkaline to help neutralize acids in vagine cowpers gland: produces mucus seminal fluid = mixture of the above three semen = seminal fluid + sperm

sperm structure: head, middle piece, tail/flagellum head contains haploid number of chromosomes nucleus surrounded by acrosome which has hydrolytic enzymes used to PENETRATEEE into the egg mitochondria are in the midpiece to give the sperm energy

how do sperms mature? the process of sperm maturation is controlled by the male sex hormone, testosterone. sertoli cells protect the spermatozoa and give nourishment. leydig cells secrete testosterone.

girls/ladies: ovaries - site of egg formation when the egg is mature, it is released into the fallopian tube

the fallopian tube is about 12 cm long, fertilizaiton takes place here uterus: where the embryo is developed. has a thick wall, size of an orange. the lining of it is called the endomytrium. the lower end is called the cervix. vagina: receive sperm, also birth canal.

ovarian cycle: