NEUR 1203 MIDTERM I

the nervous system (NS)

coordinates actions by transmitting signals to and from different parts of its body

detects environmental changes (ie. eyes detect changes in light,colour..etc.)

responds to certain events (ie. reflexes, moving out of the way)

divided into central NS and peripheral NS

Cranial Nerves

part of the somatic nervous system

12 pairs of nerves that control sensory information to CNS

connects the brain and the internal organs, thereby influencing several autonomic responses

Afferent nerves

brings sensory information in from periphery to CNS, functions include sensation to eyes, ears ,mouth ,and nose

Efferent nerves

brings sensory information out, functions include motor control over facial muscles, tongues and eyes

The 12 Cranial Nerves

1. Olfactory (smell)

2. Optic (vision)

3. Oculomotor ( eye movement)

4. Trochlear (eye movement)

5. Trigeminal (masticatory movements, facial sensations)

6. Abducens (eye movement)

7. Facial (facial movements, sensations)

8. Auditory vestibular (hearing and balance)

9. Glossopharyngeal (tongue/pharynx movement & sensation)

10. Vagus (heart, blood vessels, viscera, movement of larynx and pharynx)

11. Spinal accessory (neck muscles)

12. Hypoglossal (Tongue muscles)

Spinal nerves

functionally equivalent to cranial nerves of the head, extends from spinal cord

control and carry information about the body, trunk & limbs

each spinal nerve integrates sensory info throughout the body

Spinal Cord

bilaterally symmetrical, each vertebrae has a dorsal and ventral root

collection of fibers entering and exiting the spinal cord segment is called a root

dorsal root/fiber: afferent away from finger tips to spinal cord (in)

ventral root/fiber: efferent, carries sensory info out

Steps of spinal fibers

1. fibers entering the dorsal root bring sensory information from sensory receptors

2. fibers leaving the ventral root carry motor information to the muscles

3. collateral branches of sensory neurons may cross to the other side and influence motor neurons there

4. white-matter fiber tracts carry information to and from the brain

Law of Bell & Magendie

Dorsal spinal cord is sensory

Ventral side is motor

and they both send info to the CNS

allows inferences about location of spinal - cord damage on the basis of changes in sensation or movement that a patient experiences

Autonomic NS

divided into sympathetic and parasympathetic division

Sympathetic Division

activating system

fight or flight response

connected to thoracic & lumbar regions

spinal cord connects to autonomic control center, made up of ganglia (spinal connections to many ganglionic centre)

increased heart rate, breathing, blood pressure…etc.

Parasympathetic Division

calming system

rest & digest pathway

connects through cranial nerves 3,7,10

also connectd to sacral region of spinal cord - allows for all other processes to occur

Central nervous system

spinal cord - control centre of the entire body

vertebrae: segments of the spinal cord divided into 5 anatomical regions ( from top to bottom)

Dermatomes : segments of the body, each dermatome contains sensory nerves & motor nerves, controls most body movement, divided into sections

Cervical (C1 - C8) very top of spinal cord

Thoracic (T1 - T12)

Lumbar (L1 - L5) lower back

Sacral (S1 - S5)

can act independently of the brain, spinal relfex, autonomic movements, hard for brain to inhibit

protecting you brain

Dura mater: tough double layered fibrous tissue; encloses brain & spinal cord

Arachnoid layer: thin sheet of delicate connective tissue; follow the brains contour and creates space for CSF

Pia Mater: moderately tough membrane of connective tissue; clings to brain surface - directly attached like glue

all of these layers are called meninges

meningitis

inflammation of the meninges, bacterial infection of the meninges, particularly the pia mater and arachnoid space

CSF is implicated aswell

subarachnoid space is filled with CSF between pia mater and arachnoid layer

Intra Cranial Pressure (ICP)

inflammation puts pressure on the brain which can lead to drowsiness, delirium and coma

4 Lobes of the brain

Frontal lobe: executive function,decision making, planning, impulse control, etc.. works with parietal lobe for goal directed movement

Parietal Lobe: Tactile function, senspry & motor information processing -movement

Occipital Lobe: visual function, visual cortices

Temporal Lobe: auditory, visual, gustatory, emotion and memory

Dorsal and ventral views of the brain

Cerebrum: forebrain structure, two idendical hemispheres, responsible for most conscious behaviour - outerpart of the brain

Cerebellum (ie. little brain) controls and coordination of fine motor skills; does not initiate movements, but coordintes the timing, precision and accuracy of movements - animals that are faster or move a lot more have bigger cerebellums (ie. cheetah vs sloth)

lateral & medial view of the brain

brainstem: resposnible for unconscious behaviours, structurally continuous with the spinal cord (sits under cerebellum)

Gyri: bumps & ridges of the cerebral cortex

Sulci: cracks & valleys of the cerebral cortex (fissures are known as deep sulci)

together gyri and sulci create a larger sufrace are for the human brain

larger cortical surface area = greater cognitive functioning

lateral fissure - goes very deep and is the longest sulci in the brain, seperates the frontal and parietal lobes from the temporal lobe aka central sulcus

cerebral arteries

1. anterior cerebral artery

2. Middle cerebral artery

3. Posterior cerebral artery

   3 major arteries that supply the cerebrum

   blockage of any of these leads to regional death = stroke

   there are three so that of there is blocklage, there will still be some part of the brain that can still work but the region being blocked can completely die

Inside the brain

Gray matter: largely composed of cell bodies and capillary blood vessels; processes information and supports behaviour - outerportion of the brain

White matter: nerve fibers with fatty coverings; forms connections between cells, sends information to outer layer

ventricles: 4 cavities filled with cerebral spinal fluid, derived from blood plasma, NaCl and other salts, 3 main functions are buoyancy,cushioning, immune support ( our brains are very heavy anf=d it helps releive some weight

cells that line the walls of the ventricles are called ependymal cells and they produce CSF

Corpus Callosum

largest white matter tract that connects the right and left hemispheres

over 200 million nerve fibers that connect the 2 hemispheres; divides brain into cortical (above corpus callosum) and subcortical regions (below corpus callosum)

allows us to interact with both sides of the brain simultaneously acts as a divisor.

split brain

corpus callosum prevents cross talk between hemispheres because the language center of the brain is on the opposite side of dominant side

most of the brain is symetrucal

some functions (ie. language) is localized to one side

patients with a cut corpus callosum cant name objects in their left visual field

the brainstem

all information travels through

receives afferent nerves from all the body’s senses and sends efferent nerves to the spinal cord, it is divided into 3 distinct regions:

1. hindbrain

2. midbrain

3. diencephalon

the hindbrain

consists of..

cerebellum : controls fine motor movement

pons: connects the cerebellum to the rest of the brain

reticular formation: located at the core of the brainstem; netlike mixture of grey and white matter, helps send signals between the spinal cord and the brain

medulla: controls breathing and cardiovascular system

Midbrain

Tectum: dorsal side of midbrain, recieves sensory information from the eyes and ears, allows production of oriented movements (reflexes)

Tegmentum: superior colliculus (receives visual input) and inferior colliculus receives auditory information, inside includes…

red nuclei: motor coordination of the limbs

substantia nigra: initiates voluntary movements - dopamine system

periaqueductal grey matter - sexual behaviour and pain

forebrain

largest and most recently evolved, controls perception, movement etc. mostly found in mammals

divided into 4 parts

1. the neocortex

2. basal ganglia

3. allocortex - limbic system

4. olfactory system

basal ganglia

controls certain aspects of voluntary movements, procedural learning and habit fdormation, consists of

caudate nucleus

putamen

globus pallidus

subtsantia nigra

above the brainstem

Allocortex

deeper in the brain but still considered cortical, includes..

hippocampus: memory storage, particularly spatial memories; neurogenesis (production of new neurons)

amygdala: emotional regulation, fear acquisition, memory enhancement and activation - info feeds into HC to create memory

cingulate cortex: helps certain aspects of memory formation and recollection which helps respond to future events

Olfactory system

part of limbic system

contains olfactory bulbs - permits the sense of smell, sends sensory information directly to pyriform cortex for processing

relatively small in humans compared to other animals (eg. dogs, rats,cats)

plays a very significant role in memory formation - since its part of the limbic system, any other system goes directly to hypothalamus but this one goes through allocortex then hypothalamus

Diencephalon

hypothalamus - controls hormone production

thalamus - relay station that sends all information where it needs to go

parts of a neuron

1. soma - core region, processes information

2. dendrites - brancing extensions, collects information and sends it to the axon, the # of dendrites = amount if incoming information

3. dendritic spines: small synapses on a dendrite that serve as a point of contact with other axons

4. axon hillock: point at which the axon leaves the soma (cell body)

5. axon: carries information to other neurons through white matter tracts

6. myelin sheath: insulates axons, signals travel faster and further, electrical transmission

7. axon collaterals: point at which axon branches out: allows messages to be sent in multiple directions simultaneously

8. terminal button: stops extremely close to dendritic spine of anotjer neuron, does not touch other neurons at the end of axon collaterals

9. synapse: junctio between one neuron and the other; space between the terminal buttom and dendritic spine, where NTs are released

sensory neurons

neurons carry out the brains major functions

brings information to the brain (afferent), structurally they are the simplest type of neuron with one single dendrite on one side, cell body and single axon on the other side, subtypes of this neuron are…

bipolar neurons - retinal bipolar cell

somatosensory neurons - multipolar cell

interneurons

links sensory and motor neurons, branch extensively to collect more information subtypes include…

stellate cell (star shaped): very small, many dendrites, extending around entire cell body - in thalamus

pyramidal cell (pyramid shaped): long axon with mulitple sets of dendrites - in cortex

purkinje cell: output cell, extremely branched dendrites - in the cerebellum

Motor neurons

carry information (motor instructions) from brain into spinal cord and muscles (efferent), extensive dendritic networks to collect information from multiple sources, large cell bodies to process information, all outgoing information must pass through motor neurons to reach target muscles.

includes upper and lower motor neurons

Glial cells

cells that provide insulation and support to all neurons, they are like the parnts of neurons, and they take care of them, types of glial cells include:

1. ependymal cell: located on walls of ventricles, produces CSF and very small

2. astrocyte: provides structural support, holds neurons in place, regulates the blood brain barriers, produced in the bloodsteam , star shaped and symmetrical which allows for more blood flow, glucose and oxygen

3. oligodendrocytes: insulates axons in the CNS, assymetrical, forms myelin around axons in the brain and spinal cord, can wrap around multiple axons at once through white matter tracts

4. Shwann cell: insulates axons in the PNS, assymetrical, wraps around peripheral nerves to form myelin

wallerian degeneration

A nerve is cut or severely damaged.

The section of the nerve that is no longer connected to the main cell (neuron) starts breaking down because it can’t get nutrients anymore.

Special immune cells (like Schwann cells in the PNS or microglia in the CNS) come in to remove the debris.

In the peripheral nervous system (like in your arms and legs), Schwann cells help guide the axon to regrow. However, in the central nervous system (like the brain and spinal cord), regrowth is very limited.

neuronal repair glial cells

1. proximal axon regresses and the distal decomposes

2. shwann cells grow and form myelin

3. neurons send out axon sprouts

4. shwann cells shrink and form a path

   sometimes axons get lost and projects somewhere else or never comes, repair is much less common in CNS due to complexity and it does not have shwann cells

how do neurons communicatea?

axons carry information that connects neurons to each other

nerves when outside the CNS and tracts within the CNS

neurotransmission occurs in two steps

1. electrical

2. chemical

   for on neuron to communicat with another neuron, it must use both electrical and chemical signals

membrane potential

part of electrical communication

each neuron has a resting membrane potential - at rest the cell has no stimulus

this occurs because the cell is negative charged inside and positively chathed outside

cell membranes are permeable, it is difficult to pass through which is why cells travel through channels

resting potential is -70mV

maintaining membrane potential

large protein anions are made inside the cell and cant leave ( negatively charged)

ungated potassium and sodium channels are free moving positive ions

travel through a potasium sodium pump

electrochemical gradient

help neurons send signals by controlling ion movement. Ions move due to two forces:

1. Electrical force (opposites attract, like charges repel).

2. Chemical force (ions spread from high to low concentration).

At rest, the neuron is more negative inside. When activated, ions move, changing the charge and creating a nerve signal.

potential changes in electrical communication

without stimulus a cell will remain at -70mV

a stimulation is required to elicit a change in membrane potential

hyperpolarization: membrane potential is exagerated, so difference between inside and outside are greater

depolarization: membrane potential is diminished, so difference between inside and outside are lessened

stimulus - opens channels

actrion potential

brief but very large, reverses the polarity in the axons membrane

the inside of the cell becomes positive, relative to the outside which becomes negative

this change is abruptly reversd, thanks to an influx of potassium and then goes back to -70mV

reaching threshold

neurons receive both excitatory and inhibotry inputs: excitatory pos-synaptic potentials (EPSP) and inhibitory post-synaptic potentials (IPSP)

spatial summation: presynaptoc neurons release NT at different locations, combined signals trigger an action potential

temporal summation: single presynaptic neuron releases NT repeatedly over a short period of time, overlapping signals add up to trigger an action potential

initiation of action potential

when EPSP reaches -50mV which is the threshold to trigger a response

large influx of sodium to do channels opening and potasium leaves the cell

all or nothing —> continues until inside the cell reaches +30mV

what happens at -50mV?

Sodium and potassium channels are gated until -50mV is reached

sodium channels are faster and open first, then a second gate closes once reached +30mV no more sodium at peak action potential

potassium channels are slower and take longer to close = repolarization

Action Potential Steps

1. stimulus - signal or change that triggers cell to respond

2. threshold (-50mV) - minimum charge needed for the neuron to activate and start sending a signal

3. depolarization (influx of sodium) - sodium rushes into the neuron making it positively charged

4. peak ( + 30mV) - chage inside the neuron reaches its highest point during activation

5. repolarization - potassium moves out of the cell brining the charge back down

6. refactory period - neuron briefly recovers, can fire again but would need an even stronger stimulus

7. returning to resting state - neuron goes back to -70mV ready for next signal

action potential propogation

In myelinated neurons, the signal jumps between gaps (nodes of Ranvier) for faster transmission (saltatory conduction).

if we have a larger action potential but our axons are not very large/thick, myelin doesnt cover the whole axon

chemical transmission

how information is passed to the next cell? through the release of neurotransmitters

NTs are released in the synaptic clef (space between two terminals)

NT = chemicals that can be excitatory or inhibitory

vesticle: storage of NT

synaptic cleft: space between button and spine

post-synaptoc receptor: binding side of neurotransmitter

4 main criteria for a molecule to be classified as a neurotransmitter

1. must be synthesized in the neuron or otherwise be present in it

2. when the neuron is active the transmitter must be released and produce a response in some target

3. the same response must be obtained when the transmitter is experimentally placed on the target

4. a mechanism must exist for removing the transmitter from its site of action after work is done

   all NT are chemicals but not all chemicals are NT

types of NT

1. monoamine: dopamine, norepinephrine, epinephrine, serotonin and histamine

2. amino acid: GABA, glutamate, glycine, D-serine

3. Peptide: spmatostatin, subtance P

4. Transmitter gases: nitric oxide, carbon monoxide

4 steps of chemical transmission

1. synthesis - synthesized from DNA and stored in vesicles

2. Release — transported to pre-synaptic membrane, released in response to action potential

3. receptor action: activates target receptors on post synaptic membrane

4. inactivation: 4 different ways that the NT is taken back into terminal or stops working

removal of NT’s

can be removed or inactivated in four main ways:

1. Reuptake – The NT is sucked back into the neuron that released it (like recycling).

2. Enzyme Breakdown – Special enzymes break down the NT (like cutting it into pieces).

3. Diffusion – The NT drifts away from the synapse (spreads out naturally).

4. Glial Cell Uptake – Nearby support cells (glia) absorb and remove the NT.