Progress test 2 Flashcards
Function of the Nervous System
Senses the environment and the appropriate response.
What does the Central Nervous System (CNS) and the Peripherial Nervous System (PNS) consist of?
The CNS consists of the brain and the Spinal Cord which are each composed of Neurons and Gila.
The PNS consists of peripherial nerves and ganglia which is also composed of neurons and Gila.
What are neurons and what are there four key structures?
Neurons are cells specialised for transmission of information. The four key structures are the dendrites (KS) which recieve input from other neurons and sends to the cell body (KS) of the neuron. The cell body contains the necleus and organelles. the cell body is the site of summation of input. the axon (KS) carries the electrical impulses and may not be insulated with myelin. The axon terminal (KS) is for the transmitter release.
What are the zones of the nervous system and what do each do?
The Input Zone which consists of dendrites and cell body. this recieves chemical signals from other neurons.
The Summation Zone concists of axon hillock and functions as the summation of inputs.
The Conduction Zone consists of an axon and carries electrical signals around the nervous system.
The Output Zone consists of axon terminals and its finction is the contact withg input zone of other neurons or effectors. This releases neurotransmitters chemical signals)
What are the 4 morphological types?
The Anaxonic (axonless), which has no distinct axon and all processes look alike
The Unipolar type shows one process emanate (to come out of a source) from the body and then branches into dendrite and axon.
The multipolar has multiple processes emanate from the cell body
The Bipolar type has 2 processes emanate from the cell body.
What is the Gila?
Support cells for neurons
What are the 4 types of Gila? (Note: there are 4 types in the CNS, 1 in the PNS.)
Astrocytes (CNS): supply nutrients to neurons, ensheath blood capillaries, injury response
Microglia (CNS): immune cells of the CNS, engulf microorganisms and debris.
Ependymal cells (CNS): line fluid-filled spaces of the brain and spinal cord. Have cilia to circulate cerebrospinal fluid (CSF)
Oligodendodrytes (CNS): support nerve fibres, ensheath (enclose in a sheath) neurons in the CNS with myelin
Schwann Cells (PNS): support peripheral nerve fibres - ensheath them with myelin (similiar to oliogondendrocytes but in the PNS)
What do these mean (CNS)
(Nuclues, Tract, Grey Matter, and White Matter
Nucleus: group of cell bodies in the CNS
Tract: group of axons in the CNS
Grey Matter: group of cell bodies in the cerebral cortex (spinal cord)
White Matter: group of axons in the cerebral cortex
What do these mean (PNS)
(ganglion, nerve, myelin)
Ganglion: group of cells bodies in the PNS
Nerve: Bundle of axons in the PNS
Myelin - Lipid wrapped around the axon to inc conduction velocity (nodes of Ranvier in between)
What is a Synapse and when does this occur?
Communication between neurons - occurs at the sypnatic cleft.
Electrical signals (pre-sypnatic axon) > chemical signal (synapse) > electrical signal (post-sypnatic dendrite or cell body)
Where does the information flow into and out of the nervous system
Information flows in the both directions, Using SAME.
Afferent: Ascending infromation - information going into the brain (sensory)
Efferent: descending information - information coming out of the brain (motor)
(Sensory - Afferent - Motor - Efferent)
What is the difference between Somatic and Autonomic?
Somatic: Aware of conscious sensation (afferent) and control over voluntary movement (efferent)[skeletal muscle]
Autonomic: Unaware of unconscious sensation (afferent) and no control over involuntary movement (efferent)
[blood pressure]
NOTE: Afferent = conducting or conducted inwards towards something // Efferent = conducted or conducted away from something
What makes the Somatic Efferent and where are they?
2 myelinated neurons between the brain and the effector (skeletal muscle)
-upper motor neuron: cell body in the brain, axon in the spinal cord
-lower motor neuron: cell body in the spinal cord, axon in the spinal nerve
-snyapse onto effector muscles (skeletal muscle)
Brain > spinal cord > spinal nerve
Neurotransmitter - Ach
What is the autonomic efferent? What is its 2 divisions and what are the effectors?
Involuntary movement/control that is divided by 2 divisions (parasympathetic and sympathetic). The effectors are the smooth muscle, cardiac muscle, glands, and the adipose. The autonomic efferent consists of 3 neurons (2 myelinated, 3 unmyelinated
ACh for neuron 2; ACh (parasympathetic) or NE(sympathetic) for neuron 3.
Neuron 1 has a cell body in the brain and axon in the brain or spinal cord. (IGNORE NEURON 1)
Neuron 2 has its celll bodyin the brain or spinal cord (CNS) and acon in the peripherial nervous system (PNS)
Neuron 3 has its cell body in an automatic ganglion) and axon in the peripherial nervous system.
What do the 2 divisions of CNS do? (sympathetic nervous system and the parasympathetic nervous system)
The sympathetic nervous system prepares the body for an acute stress response (increased heart rate, etc.)
The parasympathetic is the opposite and prepares it for restful situations (decreased heart rate, etc.)
What 2 parts make up the Parasympathetic Nervous System (autonomic)?
Preganglionic Neuron: Cell bodies in cranial (brainstem) and sacral (spinal cord) levels. The axon is long and myelinated and synapses occur using acetylcholine (ACh)
Postganglonic Neuron: Cell bodies in parasympathetic ganglion. The axon is short and unmyelinated and sypnases in the effector occur using ACh again.
What is Action Potential?
AP is defined as the reversal of a transmembrane voltage that is completed in 2-3 ms.
NOTE: Establishing and maintaining the resting membrane potential drives electrical signalling
What are the 3 types of ion channels? (gating)
Chemical ion gating - cell body/dendrites
Voltage gating - axon (Na, K), axon terminals (Ca)
Mechanical gating - physical distortion
NOTE: In neurons, they are chemically gated at the cell body and axon hillock, and voltage gated in the axon.
What are the Local Potentials (AKA graded potentials) and their basic features?
Defined as the opening of ion channels in response to chemical signalling from a synapse. Can be excitatory (depolarisation) or ingibitory (hyperpolarisation).
Not actively propagated - magnitude decreases at site away from initiation.
How does summation interact with local potentials?
Effect of local potentials is summated temporally (one after the other in time) and spatially (happening at the same time next to each other)
Summation occurs at the axon hillock: there is a high density of voltage gater NA channels.
For an AP to be generated, the net voltage change must be over 10mV/threshold.
*summed local potentials
Wave of depolarisation from local potential opens (Na channels)
If this meets threshold (from -70mv > -60mv at least)
Suddenly open many voltage gated Na+ channels
This is how an action potential is generated.
How do Action Potentials occur?
Depolarisation to threshold, activation of voltage-gated Na channels, Na+ channels close (inactivation) K+ channels open (activation)
What happens to the RMP during action potential
voltage-gated Na channels are closed at RMP. When the Na+ channels close and the K+ channels reopen, it leads to the repolarisation of the membrane potential back to the RMP and at the end the RMP is restored.
What are the 2 types of refractory period of the axon.
Absolute refractory period = no possible new AP (no matter how large stimulus.
Relative refractory period = only large stimulus generates AP
Due to V.g sodium channel inactivation
Prevents AP propagating backwards.
What happens when Action Potential is using unmyelinated axons?
Ap propagates by spreading graded depolarisation to subsequent segments
Na+ (sodium) spreads laterally >
This gradually/progressively brings the next ‘segment’ to threshold
AP cannot move backwards
Relatively slow (1-5m/s)
Inadequate to meet body’s changing needs.
What happens when Action Potential is using Myelinated axons (similiar to unmyelinated axons)
Ap develops in one segment
Local current brings depolarisation to following segment (meets threshold) Na+ influx > Ap propogated (etc.)
Prior segment then repolarizes
Why is Myelin good for Action Potential
Myelin acts as an insulator. Meaning the GAPS between the myelin (nodes of ranvier) are excellent conductors. Depolarisation essentially “jumps” from node to node = ‘saltatory conduction’ which is resulting in increased conduction velocity.
What is a Synapse and a Sypnatic Cleft?
Synapse: Junction between a (pre-sypnatic) nerve terminal and a (post-sypnatic) cell - either a muscle/nerve.
Sypnatic Cleft: The physical gap between pre- and post-sypnatic cell
-Chemical sypnatic transmission turns electrical impulses into a chemical message
-occurs via the release of neurotransmitters
-once bound to their post-sypnatic receptors, the neruotransmitters open + close various ion channels to induce local changes in the membrane potential (i.e. local potentials)
-These may or may not lead to an AP in the post-sypnatic cell.
NOTE: Electrical > Chemical > electrical
What is the Sypnatic Transmission process?
Action potential arrives at the axon terminal, and triggers the opening of voltage gated calcium channels.
Calcium ions diffuse into the axon terminal, and triger sypnatic vesicles to release ACh by exocytosis.
ACh diffuses across sypnatic cleft, binds to ACh-gated sodium ion* channels, and produces a graded depolarization.
Depolarization ends as ACh is broken down by AChE into acetate and choline.
Choline reabsorbed from the sypnatic cleft into axon terminal and uses it to synthesize new molecules of ACh.
How can postsypnatic events be excitatory or inhibitory and how they summate.
Summation can be either
-temporal (one after another in time) or
-spatial (muliple inputs in different sections of the neuronal cell membrane).
Summation of the IPSPs and EPSPs may or may not bring the membrane to threshold and result in an action potential… but they increase the probability of one being produced
EPSPs produced when transmitter is ACh or glutamate
IPSPs is produced when transmitter is GABA - alcohol
There are 2 special cases of sypnatic transmission. what are they?
Electrical sypnases and the Neuromuscular junction
What is an electrical synapse?
a gap junction consisting of a field of connexin pores that pass ions and signaling molecules directly from one cell to another without passing through the extracellular fluid
Gap junction: join the presypnatic cell and post sypnatic cells which are so close together
-allows the transmission of ions between cells
-allows current to flow from the presypnatic cell to the post sypnatic cell
Electrical signal is NOT transformed into a chemical signal to cross the synapse. Voltage change in post-sypnatic cell = same as pre sypnatic. No signal modulation due to free flowing charge.
Whats the difference between the transmission at the nerve-nerve neuromuscular junction compared to the nerve-muscle neuromuscular junction?
Nerve - Nerve
Synapse size small
Input: can recieve thousands
probability of bringing to threshold: unlikely
Post sypnatic potentials: IPSP or EPSP
Neurotransmitter used: Many
Location of AP initiation: At the axon hillock
Nerve - Muscle
Synapse size: large
Input: each fibre recieves input from only one neuron at one site
probability of brining to threshold: very likely
Post sypnatic potentials: Only EPSP
Neurotransmitter used: Only ACh
Location of AP initiation: Neuromuscular junction, not hillock
What is the anatomy of a Spinal Cord?
Starts at foramen magnum (hole at base of skull). meninges create “sac” inside spine cavity (within vertebrae - filled with CSF
Non - neural tissue
-Conus medullaris - tapered cone where the spinal cord terminates/ends
-Filum terminale - fibrous, anchors spinal cord.
What does the spinal nerve consist of? (pairs, cervicals, thoracic, lumbars, sarcals, coccygeals)
31 pairs (one segment of the spinal cord gives pair (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
Exception: cervical nerves due to there being only 8 cervical spinal nerves but only 7 cervical vertebrae.
Nerves exit at the appropriate level of origin. Cauda equina = large collection inferior to the end of the spinal cord.
What are the components and the direction of information flow of the spinal cord.
Components:
Dorsal root ganglion = unipolar cell bodies
Spinal nerve
Autonomic cell bodies = lateral horn
Somatic cell bodies = ventral horn
White matter tracts = axons (dorsal column pathway
Direction of infrormation flow:
Sensory afferent = via dorsal path
Motor efferent = via ventral path
What is sulcus and fissure?
Sulcus = furrow ( A furrow in the bone surface that runs along the length of a vessel or nerve, providing space to avoid compression by adjacent muscle or external forces)
Fissure = deep sulcus
What would happen if there was damage to the Ventral horn? (Ventral = motor/efferent information)
Paralysis of muscles supplied by somatic motor neurons from spinal cord segment on the same side
If there was damage to the dorsal side (dorsal = sensory/afferent information (e.g dorsal root ganglion or dorsal column pathway)
Lots of sensation from regions of the body supplied by sensory from this spinal cord segments, on the SAME side.
What do spinal nerves do?
Spinal nerves carry afferent and efferent information
Spinal nerves split into 2 branches:
1) Dorsal ramus = efferent to the back; afferent from the back
2)Ventral ramus = efferent from the front; afferent from the front. => this splits into Rami communicans which take information to and from the sympathetic ganglion*
How do Fasicles, Axons and Nerves interrelate and differ?
Axons are covered with endoneurium
Axons bundled together to from fascicles
Fascicles are covered with perineurium
Fascicles bundle with blood vessels to from a nerve
Nerves are covered with epineurium
What are the 3 layers of the meninges
- Dura mater
- Arachnoid mater
- Pia mater
What makes the Dura mater (outermost)
The dura meter is dense and fibrous. It consists of 2 layers (inner and outer).
Inner layer forms dural folds
What is the function of Dura mater? (or dural folds)
seperates major divisions of brain, provides stability.
-Falx cerebri: seperates cerebral hemisphere, median plane
-Flax cerebelli: seperates the cerebellar hemispheres, median plane
-Tentorium cerebelli: separates the cerebrum from the cerebellum, horizontal plane
What does the Venous sinuses between layers do?
collects 1) venous blood from the brain and 2) ‘old’ CSF in some places
What is the Arachnoid Mater (middle)?
Sits beneath dura mater and above pia mater
Doesn’t extend into sulci of the brain
Containes blood vessels
2 key features
1. arachnoid granulations
-perforate inner layer of dura mater
-Drains ‘old’ CSF into the venous sinuses
- subarachnoid space
-space between the pia + arachnoid layers
-filled with CSF
What is the Pia Mater (innermost) and what does it do?
Innner layer of the meninges
Trasparent + delicate
Blood vessels in the subarachnoid space sit on top of pia mater
Adheres to the brain and follows gyri (hills), and extends into the sulci (valley).
NOTE: meninges of spinal cord have same structure as the meninges of brain.
What is the ventricular system and what does it do for the brain?
A network of interconnected spaces (ventricles) within the brain and filled with cerebrospinal fluid (CSF) which:
1) nourishes + protects the brain
2) transport nutrients + waste. found within the subarachnoid space
Spaces are lined by ependymal cells (glia cell) which circulates the CSF w/ waving cilia.
CSF is produced by the choroid plexus within the ventricles.
What is the path of the cerebrospinal fluid (CSF)
- Lateral ventricles: 2 of them - 1 in each cerebral hemisphere
- 3rd ventricle: located deep in the brain (diencephalon)
- Cerebral aqueduct: connects the 3rd ventricle to the 4th ventricle. Located in the brainstem (mid brain)
Then goes to the subarachnoid space where it flows around the brain and spinal cord via… - The central canal
> CSF exits through arachnoid granulations into benous sinus.
What do these LOBES mean?
(BE, D, E, and AB) BRAIN LOBES DIAGRAM
BE = Frontal lobe
D = Parietal lobe
E = Occipital lobe
AB = Temporal lobe
What to the 4 cerebral lobes do? (Frontal, Parietal, Occipital, Temporal)
Frontal lobe: motor, language, personality. (primary motor cortex: voluntary movement)
Parietal lobe: somatosensory (primary somatosensory cortex)
Occipital lobe: vision
Temporal lobe: memory, hearing
What are the major Gyri, Sulci, and Fissure? BRAIN LOBES DIAGRAM
Gyri
A= Precentral gyrus
C= Postcentral gyrus
Sulci
B = Central gyrus
BD = Lateral sulcus
BF = Parieto-occipital
Fissure
BG = Transverse fissure
NOTE: AE and AD make the brainstem
What are the 3 types of Tracts?
Commissural - axons cross side to side (bidirectional) example is the Corpus Callosum
Projection - between cerebral cortex and other regions of the CNS. Example: Corticospinal tract - controlling movements of arms, legs, trunk
Association (axons travel between brain areas on the same side within the cerebral cortex)
Short + Long Distance
What is the difference between reflexes vs voluntary movement?
- Reflexes are reproducible, rapid, and automatic responses to external stimuli, whereas voluntary movements have a wide variety of different movements
- Spinal reflexes use a single neural circuit that only goes as high as the spinal cord, whereas coluntary movement requires complex patterns of sensory and motor processing in cortex through muliple pathways
- Reflexes do NOT require involvement of higher brain centres, whereas voluntary movement are initiated in the BRAIN… hence damage taken to the brain areas prevents voluntary movement, however, reflexes can still take place.
Memory Aid: “lets all have fun”
Legs, arm, hand face
What does the Hommunculus do?
It’s a map demonstrating the proportional representation of the somatosensory or motor neurons on the cortex
What does the hommunculus show us?
Specific regions of the cortex recieve sensory input (somatosensory) from or controls (motor) SPECIFIC regions of the body.
Largest areas of the somatosensory or primary motor cortex are occupied by neurons projecting to muscle capable of finest + most complex movements.
Finer control/sensation = more laterally located
What are the 2 key motor pathways for voluntary movements
Corticospinal tract
Functions as the voluntary movement (efferent). This starts at the primary motor cotex and ends at the periphery
Dorsal/posterior column pathway
Functions as the somatosensory pathway (afferent) = specifically fine touch/2 point discrimination. it starts at the periphery and ends at primary somatosensory cortex.
What happens when damage occurs at the primary motor cortex or the somatosensory cortex?
Damage to the motor cortex = muscle weakness and paralysis in region of the body corresponding to location of damage ON OPPOSITE SIDE
Damage to the somatosensory cortex = ascending info has nowhere to go = lack of perception of touch in region of body corresponding to location of damage ON OPPOSITE SIDE.
Spinal cord = same side; cortex = opposite side (because it CROSSES over at the medulla oblongata)
REFELCT BOTH THE CORTICOSPINAL PATHWAY AND THE DORSAL/POSTERIOR COLUMN PATHWAY
Yea boi
REFLECT ON THE STRETCH REFLEX (monosypnatic) AND THE WITHDRAWAL REFLEX (polysypnatic), ALONg WITH THE VOLUNTARY MOTOR CONTROL LOOP
Yurr
What are the major steps in the voluntary control of movement?
Frontal cortex (decision making) > premotor cortex > Primary motor cortex (w/ info from cerebellum + basal nuclei) > Axons down corticospinal tract *upper motor neuron > Lower motor neuronwhich sypnases onto muscle fibres > generate force that moves limbs > As limb is moved, proprioceptor neurons sned sensory info to cerebellum > Is recieved in the somatosensory cortex
how does the primary motor cortex controls force by?
Recruitment (motor neurons and therefore motor units activated)
Frequency (at which AP are fired) > This helps to modulate activity pattern
What is the cerebellums role and coordinator
Helps plan, execute and learn motor programs. It intergrates sensory info (proprioceptive neurons) with planned events.
Modifies ongoing activity to make movements smooth and accurate. Its also key for control of posture, balance and body position. Disorders: various forms taxia, e.g:
- Drunken gait
- Dysarthria (slurred speech)
- Dysmetria (difficulty judging distance)
