Systems neuro

Synapse

A site where one cell communicates with another cell

axon varicosity

A swelling in an unmyelinated segment of axon containing mitochondria and in some cases, synaptic vesicles. can release transmitter.

en passant synapse

axon stimulates a synapse secondarily on its way to another neuron

spine synapse

synapse occurs on a dendritic spine

Axodendritic

axon to dendrite

Axosomatic

axon to cell body

Axoaxonic

axon to axon

Dendrodendritic

dendrite to dendrite

electrical synapse

Presynaptic cell → ions/current through gap junctions → postsynaptic cell.

There is no neurotransmitter crossing a synaptic cleft.

Chemical synapse

Electrical signal in presynaptic neuron → chemical signal in synaptic cleft → electrical or biochemical response in postsynaptic cell.

Chemical synaptic transmission

1. Action potential reaches axon terminal.

2. Terminal depolarizes.

3. Voltage-gated Ca2+ channels open.

4. Ca2+ enters the presynaptic terminal.

5. Ca2+ binds synaptotagmin.

6. Synaptotagmin interacts with SNARE proteins.

7. SNAREs cause synaptic vesicle and plasma membrane fusion.

8. Neurotransmitter is released by exocytosis.

9. Neurotransmitter diffuses across the synaptic cleft.

10. Neurotransmitter binds a postsynaptic receptor.

Important relationship:

More presynaptic Ca2+ entry → more neurotransmitter release.

What happens if presynaptic coltage-gated Ca2+ channels are blocked

less Ca2+ entry → less synaptotagmin activation → less SNARE-mediated fusion → less neurotransmitter release → weaker postsynaptic effect.

Neurotransmitters

Synthesized in neurons.

Released from presynaptic cells following depolarization.

Bind postsynaptic receptors and cause an effect.

Major categories of NT

Amino acids

Neuropeptides

Biogenic amines

Acetylcholine

Miscellaneous transmitters

A single neuron can release more than one neurotransmitter.

The same neurotransmitter can have different effects on different target cells because the receptor subtype matters.

ionotropic receptors

The receptor itself is an ion channel.

Ligand binds → channel opens or closes → ions move.

Fast and direct.

metabotropic receptors

The receptor is a GPCR.

Ligand binds → G protein → intracellular signaling/second messenger → cell response.

Slower and indirect.

Acetylcholine

A neurotransmitter that enables learning and memory and also triggers muscle contraction.

Ionotropic.

Nonspecific cation channel.

Can conduct Na+, K+, and sometimes Ca2+.

Excitatory in your course.

Found in skeletal muscle, autonomic neurons, and CNS.

Activated by nicotine.

α1

Gq → PLC

Major lecture location: smooth muscle of blood vessels to skin and gut

Effect: vasoconstriction

α2

Gi → ↓ cAMP

Major lecture location: adrenergic axon terminals

Effect: inhibits norepinephrine release

β1

Gs → ↑ cAMP

Major lecture location: heart

Effect: increases heart rate and contraction strength

β2

Gs → ↑ cAMP

Major lecture location: blood vessels to heart and skeletal muscle

Effect: vasodilation

Gi

inhibits adenylyl cyclase → ↓ cAMP.

Gs

stimulates adenylyl cyclase → ↑ cAMP.

Gq

PLC pathway

Muscarinic Receptors

Metabotropic GPCR.

Linked to second-messenger signaling.

Found in smooth muscle, cardiac muscle, glands, and CNS.

Can be excitatory OR inhibitory depending on receptor subtype.

Muscarinic subtypes

M1, M3, M5 → Gq family

M2, M4 → Gi family

Central nervous system

brain and spinal cord

peripheral nervous system

afferent branch + efferent branch

Efferent branch motor division

sketal muscle, ->voluntary

Efferent branch autonomic division

smooth/cardian muscle, glands -> involuntary

Sympathetic nervous system

the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations

Parasympathetic nervous sytem

the division of the autonomic nervous system known as the "resting and digesting" system. it causes a general decrease in body activities such as heart rate, and blood pressure and an increase in blood flow to the GI tract and an increase in digestive function; because the paraganglionic neurons all originate from either the brain or the sacram, it is also known as the craniosacral system

Enteric nervous systems

Part of nervous system responsible for digestive system.

Spinal cord

mediates information flow between brain and body (both directions).

Nucleus

a group of neuronal cell bodies within the CNS

Tract

bundle of axons in the CNS

Nerve

a bundle of many axons in PNS, contains myelinated and unmyelinated axons enclosed in connective tissue; may be sensory, motor, or mixed; classified as cranial vs spinal.

Ganglion

a group of neuronal cell bodies outside the CNS.

White matter

shiny, bright myelinated axons. In the brain, it is inside,

Gray matter

Dulled, dentrites, cell bodies, unmyelinated axons. In the spinal cord,

Afferent branch

Body/receptors → CNS

Sensory information coming in.

Efferent branch

CNS → effectors

Information going out.

Autonomic division

smooth muscle, cardiac muscle, glands

Enteric nervous system

digestive organs

Arrangement of White and gray matter in the brain and spinal cord

Brain = gray OUT, white IN

Spinal cord = gray IN, white OUT

Main functions of spinal cord

Mediates spinal reflexes.

Carries information between brain and body.

Dorsal side of spinal cord

Receives afferent/sensory signals through the dorsal root.

Somatosensory neuron cell bodies are in the dorsal root ganglion.

Ventral side

Sends efferent/motor signals through the ventral root.

Motor neuron cell bodies are in the ventral horn.

DAVE

Dorsal

Afferent

Ventral

Efferent

Simple patellar reflex

Sensory neuron → motor neuron.

two-neuron reflex.

Withdrawal reflex

Sensory neuron → interneuron(s) → multiple motor neurons.

The response must activate some muscles and inhibit others for coordination.

Divergence

One neuron sends output to many downstream targets.

Ascending tracts

Carry afferent/sensory information toward the brain.

Descending tracts:

Carry efferent/motor information away from the brain.

Ipsilateral

on the same side of the body

Contralateral

on the opposite side of the body

medula oblongata

Regulates breathing, heart rate, and blood pressure.

Pons

Communicates between medulla, cerebellum, and forebrain.

Cerebellum

Coordinates motor behaviors, controls many higher processes.

Cerebral cortex

outer region of the cerebrum, containing sheets of nerve cells; gray matter of the brain

Corpus callosum

the large band of neural fibers connecting the two brain hemispheres and carrying messages between them. white matter

Primary motor cortex

Controls discrete skeletal muscles.

Stimulation produces specific movement on the opposite side.

Damage can cause paralysis of voluntary movement. (rarely regained)

Reflexes can remain intact.

Premotor cortex

Coordinates movements of groups of muscles.

Damage causes loss of skilled movement that may often be relearned.

Primary somatosensory cortex

Receives primary input from touch, temperature, and pain receptors in skin and muscle on the opposite side.

Damage can cause loss of sensation.

Somatosensory association area

Interprets sensation and integrates it with memory.

Damage can impair identification/recognition, which may be relearned.

Primary area

receives/handles the basic signal

Association area

interprets/integrates the information

MOTOR AND SENSORY HOMUNCULI

Different body regions receive different amounts of cortical territory.

The cortex is spatially organized according to body region.

VISUAL CORTEX

Receives input from optic pathways and is activated by visual stimuli.

Thalamus

Filters and sorts sensory input.

Routes information.

Think "relay station."

Hypothalamus

Major homeostasis regulator.

Functions in stress response, HPA(hypothalamus,pituitary,adrenal) axis, food intake, body temperature, ion/water balance, circadian rhythms, and pituitary regulation.

Hippocampus

Learning and memory.

Amygdala

A limbic system structure involved in memory and emotion, particularly fear and aggression.

olfactory bulb

the first brain structure to pick up smell information from the nose

sympathetic nervous system

Fight or flight.

Most active during stress or physical activity.

Increases heart activity and breathing.

Redirects blood toward working muscles.

Reduces immediate digestive investment

parasympathetic nervous system

Rest and digest.

Most active during rest.

Supports maintenance, digestion, secretion, and energy conservation.

DUAL INNERVATION + ANTAGONISTIC ACTION

Many organs receive both sympathetic and parasympathetic innervation with opposing effects.

Heart:

Sympathetic → increases heart rate.

Parasympathetic → decreases heart rate.

Pupil:

Sympathetic → dilates.

Parasympathetic → constricts.

pupil

The pupil is a HOLE/OPENING in the iris, not a muscle.

Bright light:

Parasympathetic stimulation → circular iris smooth muscle contracts → pupil constricts.

Dim light:

Sympathetic stimulation → radial iris smooth muscle contracts → pupil dilates.

Circular = drawstring → closes opening.

Radial = spokes pulling outward → opens it.

Preganglionic neuron:

Cell body in CNS.

Axon goes from CNS to autonomic ganglion.

Postganglionic neuron:

Cell body in ganglion.

Axon goes from ganglion to target organ.

Parasympathetic postganglionic neuron:

Usually ACh → muscarinic receptor on target.

Typical sympathetic postganglionic neuron:

Usually NE → adrenergic receptor on target.

AUTONOMIC NEUROTRANSMITTERS

acetylcholine and norepinephrine

Norepinephrine

A neurotransmitter involved in arousal, as well as in learning and mood regulation

Adrenergic Receptors

receptor sites for the sympathetic neurotransmitters norepinephrine and epinephrine. diverse effects based on receptor subtype. metabotropic GPCRs.

ADRENAL MEDULLA EXCEPTION(not dual innervated)

Adrenal medulla is sympathetic only.

Preganglionic sympathetic neuron releases ACh onto nicotinic receptors on chromaffin cells.

Chromaffin cells release epinephrine into the bloodstream.

SYMPATHETIC VASCULAR CONTROL

Skin/gut vessels:

α1 → vasoconstriction.

Heart/skeletal-muscle vessels:

β2 → vasodilation.