Physiology Lecture (PNS) Flashcards
PNS
Function - Connects the CNS to the limbs + body + Skin + Organs
- PNS = not protected by bone of the BBB
- Divided into the somatic and autonomic nervous system
Location - Outside the CNS (outside the brain and the SC)
CNS vs. PNS
CNS - brain + Spinal cord
PNS - Peripheral nerves
What gives rise to the PNS
Neural crest cells gives rise to PNS during emroyogneisis (PNS comes from from nueronal crest cells)
- Neuronal crest cells = migrate to different places in the body to become PNS (migrate from the dorsal side of the nueronal tube)
Nueronal tube = becomes spinal cord
Characteristics of Nueronal Crest cells
- Nueronal crest cells = transient –> Only found during development
- Nueronal crest cells = stem cells –> differentiates to many nueronal and non-nueronal types of cells
- Example - Becomes all peripheral nerves + glial cells + Dorsal root ganglion + sympathetic/parasympathetic + entric + non-nueronal cells (melanocytes)
Nueronal Crest cell fate
Nueronal crest cells take different pathways + terminate at many peroheral locations + differentiates into many different cell
Moleculares in PNS development
There are many molecules that have been implciated in various steps of PNS development
Steps:
1. Transcription factors (Ngn + NeuroD + Brn3a) –> Determine cell fate and specification
- Example - express Transcription Factors in muscles - can turn muscle cell to nueronal cell
- Nuetrophils and receptors (NGF/TrkA and BDNF/TrkB)
- Determines cell fate and cell survival
- Growth factors/receptors = imoortant for nuronal survival (need in cell culture to keep culture alive)
- Axon guidence molecules (netrins + sema + Silt)
- used for Axonal outgrowth + pathfinding + branhcing + targeting
- Need nuerons to extend axons = need axon guidence molecule
- Can be attractice or repulsive molecules to get axonto target tissue
- Glutamate receptors
- Used for refinment of targeting pattern (once gets to location = need to refine targeting oatter)
Division of PNS
Divides into somatic and autonomic nervous system
Autonomic nervous system
Function - Controls vesiceral functions (heart rate + digestion + breathing + Salivation + sweating + diameter of pupil + urination + Sexual arousal)
Essential for mainating homeostatsis
Divided - into sympathetic + parasympathtic + entric divisions
Major nuerotransmitters - neopinephrine + acytlecholine
Function of Autonmic nervous system
Autonmic = functions largley below level of conciusness
BUT certain events can change the level of autonmic activity (Example - emotional stress + fear + sleep + sexual excitments)
Inervations of Autonomic Nervous system
Autonomic innervates (sends axon) cardiac masucles (control heart beats) + smooth muscles + glads to regulate basic viseral porcesses
ALSO - relays visceral sensory information to CNS
ALSO - induces release of hormones that medate energy metabolism (ex. releas einsulin + glucogon) + releases things that affect cardiovascular functons (Vssopressive - conrtols blood vessle pressur)
Nuerons in Sympathetic
Sympathetic = uses a two nueron system –> Sympathetc preganglionic nuerons –> Preganglionic exit the spinal cord –> Synapse with the post ganglionic nuerons in symathetic ganglion or chromaffin cells in adrenal glands –> Post ganglionic extend their axon to get to the tissue
- Cell bodies aregate to form synapse
Cell body of preganglionic = found in thoracic and lumbar region inside of Spinal cord (then axons extend outside of spinal cord)
Nuerons in Parasympathetic
Parasympathetic = uses a two nueron system –> preganglionic fibers lie in specific nuclei in the brainstem or in the lateral hrons of the spinal cord at the sacral levels –> Axons of preganglionic projects to postganglionic fibers in galanglia (ganglia are close to viceral targets or located in them)
Preganglionic = reside in brainstem/brain or the sacral region of spinal cord —> extend axon –> synapse with cell body with oarasympathtic ganglion
Sympathtic vs. Parasympathtic nueronal synaoses
Sympathetic –> Synapse - ganglion ate far from targets
Parasympathtic –> Synpasic ganaglion are close to their targets
Parasympathetic control vs. Sympathetic control
Parasympathic - controls maintaince of activities that help conserve the body’s energy and is responsible for rest and digest
- Constrict pupils + salivation + decrease heartbeat + constrict brochi + stimulate digestive
Sympathtic divsions - Mos active during times of stress fivering the fight and flight
- Dilates pupil + inhibits salivation + relax bronchi (breathing more) + increase heart rate + inhibits digestion
Parasymoathtic vs. Sympathetic = opposite functions
Enteric Nervous System
Consists of two plexuses embded in the wall of the Tract (Myentreic Plexuys + submuscosul plexus)
- Submucosoul plecues = close to lumen of GI tract
Composed of:
1. Local sensort nuerons that detect chnages in the tension of the gut and the chemical envirnment
2. Interneuons and motor nuerons
- Motor nuerons = conrtols the muscles of the gut wall + galnd secreation + local blood flow
Regulated by the extrinci innervation form the sympathetic and parasympathetic systems
Plexues
Netrowk of nuerons
In enteric system - consists of local sensory nuerons + internuerons + motor nuerons
What is the enteric nervous system considered
Considered the second brain - number of nuerons in the gut > the number of nuerons in the Spinal cord
Semetosensory Somatic nervous system
Function - reponsivle for receivig stimuli from the external and internal envirnments + coordinates body movements
- Acts under concious control
- Somatosensory = Processes toucb + pressure + temperature + pain + itch + muscle contraction + stretch + join position
Intiation and mediation = due to dorsal root gangkion + trigenminal ganglion
Major nuerotransmitter = Glutamate
Function of CRG and trigemnal in somatic nervous system
Dorsal root ganglion + trigeminal ganglion receive and interprets sensory inforation from inside the body and from the envirnments
- Envirnmental sensation = through the skin
Sensory nuerons in somatic nervous
Cell bodies of primart snesory nuerons locate in Dorsal root ganglion –> cel body of sensory form the dorsal root ganglion
How many pairs of DRG are theer
There are 31 pairs of DRG along the spinal cord
- Each gangion inervates a certain region of the body
Image - bulbs by the Spinal cord = DRG –> see the bundles extend out of the gangion
DRG vs. Trigeminal control
Dorsal root ganglion = controls sensory for the whole body + back of head/neck
Trigeminal ganglion = controls sensory for face (Ex. what is active when have migraine)
Axons of primary sensory nuerons
Primary sensory nuerons in DRG have two axons (neuron is psudedounipolar)
Axon 1 - projects to the periphery (organs - skin/muscle/joints/verscera) to get snesory information
Axon 2 - Projects to the CNS (Spinal cord)
DRG = outside the spinal cord
DRG - have two cell bodies
Primary sensor nuerons
Neurons in the DRG
Function - first to detect infomration (first to feel in skin)
Secondary nuerons
Spinal cord nuerons
Secondary neurons Decussate (cross the midline) –L axon crosses the midline to the other side of teh spinal cord to go to the thalumus (reason why the left brain controls the right side of body and vica cersa)
Somatic nervous system synapses vs. Autonmic nervous system synapses
Top - Somatic - 1 axon –> goes to the peripheral target and to CNS (to SC)
Bottom - Autonomic - 2 nueron system (preganglionic –> ganglion –> postgangliic –> periphery
Dermatome
The area of skin inervated by a single forsal root
Each pair of DRG sends an axon to different parts of the body – creates dermatomes
Tractile + pain + termapture dermatomes bounderies can be different
Mapping dermatimes
Repsonse of each dorsal root ganglion to different stimuli can be systematically tested and the bounderies of each dermatome can be mapped
map dermatimes by recording nerves and see where they innervatate –> see reponse of each DRG to stimuli –> map bounderies of dermatimes
Overlap of dermatomes
Adjacent dermatomes can overlap because of overlapping adjacent dorsal roots
Each DRG sends an axon —> Axons can branch to cover more area of the skin - at bounderies there can be overlap between where DRG send axons
Skin somatosensory nerve endings
Mechanocorecpetors (slow adpating) –> Mekel cells + ruffiniing endings
Pain/temp (rapidly adapting) –> Meinssner + passinean corpsucles
Free nerve endings - not associated with end organs just axon sent to skin
- Senses pain + temp
Slow vs. rapid adpating
Slow - innervates the area –> nerve first AP during duration of indentation (nerve keeps firing while applying pressure)
Rapid - Nerve first during onset and offset (when pressure is applied and taken off)
Rapid vs. slow adpating - allow syou to feel uintity of pressure/touch
Organs in skin innervted by nerves
There are 4 organs in skin innervated by nerves:
1. Meissners corsulcles
2. pasinean corpsucles
3. Ruffini endings
4. Merckles disks
Different end organs allow nerve to sense different types of sensation
Neurons in the spinal cord
Afferents enter the spinal cord - DRG axons (blue) + decesning afferent from the brain (green)
Nuerons in spinal cord - Projecton uerons (brown) + interneuons (purple_ + effernet neruons (Maroon)
Spinal cord cross sections
Image - Blue on upper left = dorsal horn ; Green on lower left = ventral horn –> BOTH have axons going to spinal cord (going to different regions of the spinal cord)
Image - Right = nuerons within the spinal cord (peripheral axons synapse with spinal cord nuerons_
- Brown line = seocndary axons crossing the midline
Axons = have different termmination based on sensation –> you can guess snesory function based on termination
- Dorsal horn = termpature + pain
- Ventral hron = muscle sensation
Divion of grey matter in spinal cord
Grey matter in spinal cord is subdivided into 10 laminae based on nueronal cytoarchitectire
Example - dorsal horn = pain + temperture + itch + touch
Example #2 - venral hron = controls muscle
order of nuerons in somatic nervous system (How sensroy detects information and sends information to the brain)
Order - Primary nuerons (Dorsal root ganalion detecting information from peripshery) –> Secondary nuerons (SC _ medual) send nueron to thalmus in the brain –> terta=irary nuerons in the thatmus nucleaus which send axon to cortext in brain –> 4 nuerons in cortext
Nerons in somatic = connected ina seriors by their nerve fibers for sensory infomration trasnfering from body to cortext
Have seperate pathways to touch/position vs. pain/tempeture
Two pathways in somatic
Have two major ascedning pathways sending somatic sensory information to the cortxt:
1. pain and Tempeture
2. tact (touch and vibration) + limb perioperceotion
Perioperception
Sensation of body - controled by nerves inervating muscles
Example - close etes and can still touch nose
IF have no perioperception = can’t stand (Ex. geentic issues where you loose nerves = become paralyzed)
Pain and temperture Somatic pathway
Anterolateral system - Axon goe sto spinal cord –> synapse with DRG –> Axon cross midline –> Axon goes to thalumus –> Axon goes to cortext
Acending = goes towards the brain