Nervous System

• maintaining constant internal environment despite changes in the external environment • eg: we get cold so we shiver, we get hot so we sweat

Chemoreceptors –> chemicals (eg: taste buds on tongue) Mechanoreceptors –> pressure, vibrations and touch (pressure receptors in skin) thermoreceptors –> temperature (hot and cold receptors in skin) photoreceptors –> light (rods and cones in retina) pain receptors, nocireceptors –> cell damage/excess heat

CNS (body master control unit) 1. brain and spinal cord PNS (body link to the outside world) 1. autonomic NS (internal stimuli, involuntary process) - sympathetic NS (fight or flight) - parasympathetic NS (rest + digest) • somatic NS (external stimuli, voluntary movements, sensory info from organs to CNS and then to muscles) - sensory input (Afferent) - motor output (Efferent)

1) Sensory input from sensory receptors (PNS) is transfered to CNS. 2) integration and intepretation in the CNS 3) Conduction of signal from CNS to effector cells, muscles + glands which carry out the bodys responses (PNS) SENSORY INPUT PNS –> INTEGRATION/INTREPRATION CNS –> MOTOR OUTPUT PNS

• INPUT zone where cell recieved neural information • recieve info from environment/other neurons • conduct nerve impulses AWAY from cell body

• contains the nucleus • recieve, sort, priritize neural information

• act like a switch • trigger electrical impulses to move to the axon

• OUTPUT zone • conducts nerve impulses toward axon terminal • long cord like extension of cytoplasm, conducts nerve impulses away from cell body • larger diameter of the axon the faster the speed of nerve impulse

Allow diffusion of ion

• At hthe end • forms junctions with other cells • store NT chemicals which control transfer of neural info btwn neurons

• insulation for neurons • made up of schwann cells • nerve impulses move faster along myelinated nerve fibres than unmyelinated

• surrounds the axon, on top of myelin • formed by schwann cells and promotes regeneration of damaged azons

• Just because there is a myelin sheath doesn’t mean there is a neurilemma White matter in brain have myelin Gray matter dont have myelin (in spinal cord) White and gray matter both odnt have neurilemma which means damage to CNS is permnant

Innermost –> outermost Axon > myelin > neurilemma > Schwann

Produces the myelin sheath

Sensory neurons (afferent neurons) - relay info/stimuli thats received by sensory receptors about external/internal environment - cell bodies of sensory neurons are located in clusters called ganglia (outside the spinal cord) 2) interneurons (association neurons) - link neurons to other neurons - integrate + interpret sensory info + connect sensory neurons to outgoing motor neurons - only in brain + spinal cord 3) motor neurons (efferent neurons) - relay information to the effectors (cell/organ that responds to stimulus)

non conducting cells that are Support cells - support neurons structurally - deliver nutrients + remove waste - repair neurons in PNS - insulate neurons

Schwann cells - axon > myelin > neurilemma - has a nucleus that directs growth of myelin - gaps btwn schwan cells are nodes of ranvier

1) oligiodendrocytes - wrap around neurons making insulating sheaths - made up of myelin (white matter) • astrocytes - provide structure + metabolic support

• reflexes involuntary + unconscious • neural circuit that travels through spinal cord and provides a framework for reflex action sensory receptor –> sensory neuron –> interneuron in spinal cord –> motor neuron –> effector

change in electrical potential associated with passage of an impulse

voltage gated: open at certain membrane potential and close at others (eg: NA channels open around -55mV) ligand gated channels: open when a specific NT latches mechanically gated channels: open in response to physically stretching the membrane

1) More sensory receptors fiting, mean more action potentials = stronger stimulus 2) higher frequency of firing = stronger stimulus

node to node conduction. conduction that happens myelinated axons. 1) saves energy by decreasing use of sodium potassium pump 2) its faster which allows organism to react faster