Physio - Nervous system and Brain Functions

senses, peripheral nervous system, reflexes, action potentials, nerves, central nervous system

Action Potential

-movement of ions causes rapid change in membrane potential energy in response to a stimulus

-action potentials are ALL OR NOTHING. Once the threshold potential is reached, the neuron will have an action potential

-the intensity of the signal can increase or decrease depending on the frequency of the stimulus

note: cannot change voltage but can have more frequent stimulus for more action potential

Action Potential Steps

1. At rest

2. Stimulus applied

3. Voltage rises (depolarization)

4. Voltage falls (repolarization)

5. End of action potential (hyperpolarization)

6. Return to rest

Action Potential Step 1: At rest

-more negative charges on the inside of it than on the outside

-membrane potential = -70 mV

-this is maintained by sodium and potassium leak channels, sodium-potassium pumps, and negatively-charged proteins inside the neuron

Action Potential Step 2: Nerve is stimulated

-membrane potential starts to rise

-the type of stimulus varies depending on the function of the neuron

(ex. your eye’s optic nerve is stimulated by light)

Action Potential Step 3: Depolarization →Voltage rises

-once the threshold potential of -55 mV is reached, voltage-gated channels open and the membrane depolarizes to approximately +40 mV as sodium flows into the neuron

Action Potential Step 4: Re-polarization →voltage falls

-once it reaches +40 mV, the voltage gated sodium channels close and voltage-gated potassium channels open

-the voltage falls as potassium ions flow out of the neuron

Action Potential Step 5: Hyperpolarization (end of action potential)

-the membrane potential of the neuron drops far below its resting potential and ends up in a hyperpolarized state at -90 mV

Action Potential Step 6: Return to resting potential

-the membrane potential returns to the resting potential of -70mV by the sodium and potassium leak channels and sodium-potassium pumps

Action Potential: Refractory Period

when an axon is in the middle of an action potential, it CANNOT respond to any other stimulus, no matter how strong

note: this prevents overstimulation of nerves

Saltatory Conduction

-a “jump” on the unmyelinated nodes of Ranvier between the myelin

-these “jumps” cause faster movement

This movement….

-increases rate of propagation of an action potential

-increases speed of impulse transmission

-conserves energy for axon (100x less movement of ions) ←energy used to re-establish the Na+ and K+ concentration differences across membrane

Note:

-cannot do action potential on myelin (depolarization)

-some nerve cells are unmyelinated

Functions of the Nervous System

1. Collecting information

   a. Input from senses

2. Processing information (integration)

   a. brain

3. Motor output

   a. Structures move or respond accordingly

Neuron Structure

-Cell body: contains the nucleus and other organelles

-Dendrites: receives impulses and passes them to the cell body

-Axon: moves impulses down the neuron

note: nerves range in size from <1mm to > 1 meter long

Glial Cells of the CNS (supporting cells)

-microglial cell: immune system? pain receptors?

-atrocytes: deliver nutrients to the cell body

-ependymal cells: filters the blood to make cerebrospinal fluid (CSF)

-oligodendrocyte: contains myelin (fatty substance that helps with signal transmission)

Note: brain is not full of blood all of the time

Grey Matter

-unmyelinated

-regions with many cell bodies and dendrites

Note: fat for relying signals (communication)

White Matter

-myelinated

-regions with many axons

-the brain is your fattest organ (60% fat)

note: fat for relying signals (communication)

Gyrus

ridges on brain surface

Sulcus

grooves on the surface of the brain

Fissure

deep grooves on the surface of the brain

Prefrontal Cortex

planning, personality, short-term memory, and consciousness

Frontal Lobe

motor functions

Precentral Gyrus

primary motor cortex

Parietal Lobe

speech, vision, taste, touch, pain, body position

Occipital Lobe

Vision

Temporal Lobe

auditory, vision

Limbic Lobe (part of the cerebral cortex)

amygdala, hippocampus

Diencephalon

Thalamus, Hypothalamus

Brain Stem

Midbrain, Pons, Medulla

Cerebellum

- “little brain”

-coordinates and regulates muscle activity

-important for smooth movement, timing

-compares sensory information to directions for motion from the frontal lobe

Amygdala

-social/emotional

-decision making

Hippocampus

-learning

-long-term memory storage

-spatial memory

Hypothalamus

homeostasis

Thalamus

-all sensory info (except smell) passes through the thalamus before being processed by the cortex

Mid brain

connects the visual and auditory sensory input with spacial awareness

Medulla Oblongata

-breathing, heart rate, blood pressure

-reflex centers for vomiting, coughing, sneezing, and swallowing

Ventricles

-4 total fluid-filled cavities that contain cerebrospinal fluid (CSF)

Corpus Callosum

bands of white matter that allows communication between the 2 hemispheres of the brain (left and right side)

Pons

breathing

Protection of CNS (central nervous system)

-skeletal protection

-cerebrospinal fluid (CSF)

• everything floats in liquid that acts as a cushion to physical impact and a barrier to infections

-meninges = membranes

• dur mater

• arachnoid

• pia mater

General senses

-senses that don’t have a specialized organ dedicated to their perception

• touch, pressure

• pain

• temperature

Taste (Gustation)

-taste buds detect chemical compounds depending on flavor

-salt: Na+

-sour: H+

-sweet: sugars activate a G protein second messenger pathway

-bitter: alkaloids, etc. also activate a G protein pathway

-umami: amino acids activate a G protein pathway

Note: spicy isn’t a taste, it’s a pain (chemosthesis)

Smell (Olfaction)

-detection of airborne chemicals

1. odor molecules get trapped in mucus

2. molecules bind to proteins that keep them dissolved in the mucus and help transport them

3. Odorant-protein complex binds to a G-protein receptor on the olfactory dendrite, produce a graded membrane potential to send signals to the brain

   Note: lots of emotions + memory are attached to smell

Vision

1. light is bent by the cornea and lens before reaching photosensitive cells (rods and cones) in the retina

2. light causes structural changes to opsin molecules in the cells that trigger a G-protein pathway and membrane potential change

3. signal moves through bipolar cells to the optic nerves

4. the optic nerve sends the signal on the brain for processing

Nearsighted

-cannot see distant objects well

-eyeball is elongated

-images form in front of the retina

Farsighted

-cannot see close up objects well

-eyeball is condensed

-image forms behind the retina

Astigmatism

-eyeball shape is normal but the cornea is not a sphere or the lens is misshapen

-light traveling into the eye is distorted

Hearing

1. Sound waves are captured by the cartilage of the external ear

2. eardrum membrane vibrates

3. ear bones (stirrup, anvil, hammer) vibrate the cochlea

4. hair cells attached to the nerves in the cochlea bend, send signal to the brain

   Note: hair cells is a mechanoreceptor ←when it bends, their stereocilia open ion channels that depolarize the cells and start an action potential

Balance

-sensed by different types of hair cells in the semicircular canals

-3 tubes that detect movement in 3 planes (x, y, z)

-movement of fluid causes hair cells to bend, nerves attached to hair cells signal the brain

Cranial Nerves

-large nerves attached directly to the brain

-primarily responsible for the sensory and motor functions of the head and neck

-nerves are sensory nerves, motor nerves, or a combo of both

Spinal Cord

-initiates most reflexes

-31 pairs of spinal nerves branch out from the cord to serve all parts of the body

-contains many inter neurons

• inter neuron = a neuron that transmits signals between other neurons

Somatic Nervous System →Voluntary

-all voluntary motion of skeletal muscle

-neurotransmitter = acetylcholine

-complex network of four nerve plexuses

• cervical, branch, lumbar, sacral

-excitatory only

• tell the muscle to contract or don’t tell it anything

Autonomic Nervous System →Involuntary

Sympathetic and parasympathetic

Note: most of the time both are active

Sympathetic: Autonomic Nervous System →Involuntary

-”fight or flight”

-increased body activity due to excitement, in an emergency

-controls epinephrine (adrenaline release)

-increased heart rate, blood pressure, dilation of blood vessels, removal of blood from the digestive organs

Parasympathetic: Autonomic Nervous System →Involuntary

-”resting or digesting”

-decreased heart rate, blood pressure

-normal digestion, removal of feces and urine

-controlled largely by pons and medulla

Reflexes

-involuntary and rapid

-usually occurs to prevents injury

-direct connection between sensory input and motor input

-spinal cord controlled (no processing by the brain)

Simple Reflex

-the sensory neurons synapses directly with the motor neuron

-found more often in the autonomic nervous system

Complex reflex

-involves multiple motor neurons, sensory neurons, and inter neurons

-all somatic reflexes are complex

What happens during a concussion (on neuron level)

-neurons stretch and tear, when they get destroyed…

• they cannot communicate

• axons release toxins causing the death of other neurons

Common symptoms of concussion

-blackouts

-balance issues

-nausea

-headaches

-trouble sleeping

-blurry vision

-memory problems + thinking problems

-altered mood and behavior

-onset of anxiety and depression

Standard Treatment for a single concussion

-lots of rest (brain heals itself)

-gradual return to activities ←stop dangerous activites

Note: it will heal in matter of days or weeks

Sub-concussive hits

head injuries that don’t cause full-on concussions but can still cause damage (ex. heading a soccer ball)

Note: can result in CTE

CTE on a molecular level

chronic condition that breaks down the brain due to brain damage

1.tau proteins surrounding microtubules dislodge from microtubules and clump together

2.disrupt communication along the neuron, breaking down communication

3.tau protein spreads and eventually degrades brain

CTE stages

Stage 1: A few hot spots of tau tangles appear in isolated areas of cortex

Stage 2: Multiple hot spots appear in cortical sulci; tau starts to migrate through brain

Stage 3: Tau hot spots start to blend with one another. Tau starts accumulating in the hippocampus and amygdala

Stage 4: Dense tau tangles cover the brain’s cortex and appear in most brain regions, including the spinal cord

REM Sleep

-brain exhibited activity similar to being awake but you are unresponsive (ex. dogs moving their feet in their sleep)

Charles-Bonnet Syndrome

-patients with impaired vision or blindness that previously had vision experience vivid hallucinations

-same brain use as sight

-the brain makes up the images from memory (fills in the gaps)

-schizophrenia meds can help with this

Spinal Cord Injury

-any injury to the spinal cord that results in an alteration, either temporary or permanent, in its motor, sensory, or autonomic function

to identify..

-look at reflex responses

Synapse

1. Action potential travels down axon towards synaptic knob

2. Action potential causes voltage gated Ca channels to open

3. Calcium causes exocytosis of neurotransmitter

4. Neurotransmitter binds to stimulus gated channel and causes it to open