Nerves

The Nervous System is divided into

Peripheral Nervous System and Central Nervous System

Peripheral Nervous System consists of what?

Autonomic Nervous System + Somatic Nervous System

Autonomic Nervous System

1. Involuntary

2. Regulates homeostasis

3. Control smooth/cardiac muscle

Autonomic Nervous System consists of what?

Parasympathetic Nervous System + Sympathetic Nervous System

Parasympathetic Nervous System

Rest + Digest

Sympathetic Nervous System

Fight or Flight

Central Nervous System consists of what?

Spinal cord + Brain

The Brain

1. Grey matter

   1. outside cell bodies

2. White Matter

   1. Inside axons

3. Myelin

   1. Lipid insulation = white

4. 80% of brain used during complex tasks

What do neurons do?

Sends signals

Glial cells

Support Neurons, produce myelin

Neuron

Multipolar: Most common (1 axon, multiple dendrites)

Dendrites

Recieve Signals

Soma (Cell Body with Nucleus)

Soma (Cell Body with Nucleus)

Axon Hilcock

Start of axon where action potential begins

Myelin

1. Lipid Sheath for protection

Myelin CNS

1. CNS= Oligodendrocytes produce myelin

Myelin PNS

1. PNS= Schwann Cells produce myelin

Types of Neurons

Unipolar, pseudounipolar, bipolar

Unipolar

Single process emerging from cell body

Pseudounipolar

Single Process split into two branches (*Sensory + Simple Reflexes)

Bipolar

1 axon + 1 Dendrite (*retina + olfactory)

Glial Cells of CNS (Support)

1. Oligodendrocytes = produce myelin

2. Astrocytes: “Star Shaped”

   1. Support Neuron

   2. Form blood brain barrier

3. Microglia: Immune Cells of CNS (engulf pathogens)

4. Ependymal

   1. Lining of spinal cord, produce cerebrospinal fluid

Glial Cells of PNS

1. Schwann Cells=produce myelin

2. Satellite Cells= Support neuron bodies

   1. *Myelin = increase signal speed

1. Unmyelinated=slow, continuous (nocieptors=pain)

2. Myelinated=fast, saltatory conduction, jump at nodes

Function of Nervous System

1. Sensation: Detect Stimuli

2. Integration: Process

3. Response: Generate output

Example Pathway: Touching Water (Sensation)

1. Stimulus=sensory neurons in skin detect temperature

2. Signal initiation=Graded Potential triggers Action Potential in sensory neuron

Example Pathway: Touching Water (Integration)

3. Spinal Cord: Interneurons pass info to brain

4. Brain processing=Signal reaches thalamus and cerebral cortex (decision made)

Example Pathway: Touching Water (Response)

5. Motor Response=upper motor neurons send signal down spinal cord

6. Effector Activation=lower motor neurons stimulate muscle contraction via neuromuscular junction

Graded Potential Triggers Action Potential, which equals to?

All or nothing, once triggered=no going back

Graded potential

1. local, temporary changes in cell membrane voltage

   1. Cells use ions specifically Na+/K+ to create change differences across the cell membrane

   2. Ex: Na+/K+ pump: move Na+ out and K+ in to maintain concentration gradients

Ions go through ion channels

1. Ligand-gated=neurotransmitter stimulated (Chemical)

2. Mechanically gated=physical stimulus (Physical)

3. voltage-gated=change in voltage (Electrical)

4. Leakage channels=maintain resting potential

Resting Potential

1. Inside cell= negative

2. Maintained by Na+/K+ leak channels

The Action Potential

1. Depolarization:Na+ channels open → Na+ enters → membrane (graded potential)

2. Repolarization: K+ channels open → K+ leaves → Membrane returns to negative (action potential)

3. Hyperpolarization: Membrane briefly more negative than resting (action potential)

   1. Refractory Period: Absolute=no new action potential possible

   2. Relative= can fire but requires stronger stimulus (1-2 milliseconds)

4. Return to rest: Na+/K+ pump restores original concentrations (resting potential)

Chemical Synapse:

Neurotransmitters

Cholinergic (Acetylcholine), amino acids: glu, GABA, Gly, Biogenic=seratonin; norepinephrine; epinephrin; dopamine.

Two main types of Cholinergic (Acetylcholine)

Nicotinic (@ NMJ), muscarinic (ANS)

Amino Acids:

glu, GABA, Gly

Biogenic:

Seratonin, norepinephrine, epinephrin, dopamine

Sensory Receptors

1. Free nerve endings (pain and temp)

2. Interoreceptors (internal/organs)

3. Specialized receptor cells

4. ^^^^ALL ARE STRUCTURE

Location of sensory receptors:

1. Exteroreceptors (External/skin)

2. Interoreceptors (Inernal/organs)

3. Proprioceptors (body position + movement)

Function of Sensory Receptors

1. Chemoreceptors = chemicals

2. Mechanoreceptors = presure

3. Thermoreceptors = temperature

4. nocireceptory = pain

5. photoreceptors = light

Sensory Modalities

1. General

   1. Touch

   2. Pain

   3. Temperature

   4. Proprioception

2. Special

   1. Vision

   2. Hearing

   3. Balance

   4. Taste

      1. Smell

Special Senses

Taste, smell, hearing, balance

Special Senses: Taste

1. Taste (GUSTATION)

   1. Receptors=taste buds on tongue

   2. primary tastes=

      1. sweet → sugars

      2. salty → Na+ ions

      3. sour → H+ ions (acids)

      4. bitter → toxins

      5. umami → glutamate

   3. Signals travel through

      1. Facial nerve VII

      2. Glossopharyngeal IX

      3. Vagus X

Special Senses: Smell

1. Receptors= olfactory epithelium in nasal canal

2. Direct connection to limbic system → trigger memory/emotion

3. Travel via olfactory nerves

Special Senses: Hearing

1. Sound waves converted into Neural signals in ear

2. External ear=collects sound

3. Middle ear = amplifies osund

4. Inner ear= transdices sound

5. Ossicles

   1. Malleus

   2. Incus

   3. Stapes

6. Cochlea:

   1. Fluid movement in basilar membrane

   2. Hair cells bend

   3. Ion channels open

   4. Action potential generated

   5. *Different regions of the cochlea detect different sound frequencies

Special Senses: Balance

1. Balance detected by hair cells in the inner ear

2. Maculae= (utricle/saccule)

   1. Detect: head position linear

      1. linear acceleration

      2. gravity

3. Semicircular canals

   1. Detect: rotational movement

4. Signals travel through vestibulocochlear nerve

5. Somatosensation (Touch)

   1. Merkel cells → light touch

   2. Meissner → fine touch

   3. Pacinian → deep presure

   4. Ruffini → skin stretch

   5. Free nerve endings → pain/temp

6. Vision:

   1. photoreceptors → phototransduction → photoisomerization → optic nerve (flip image)

Sensory nerve pathways:

1. Afferent (sensory) fibers → ventral root

   1. (ARRIVES)

2. Efferent (motor) fibers → ventral root

   1. (EXITS)

Sensory Input travels from?

PNS → (Afferent) → CNS

Sensory Inputs PNS:

1. Touch, pain, temp, proprioception, taste, hearing, balance, vision, smell

Sensory Inputs PNS: Touch

Encapsulated nerve ending

Sensory Inputs PNS: pain

free nerve endings

Sensory Inputs PNS: Temp

Free nerve endings

Sensory Inputs PNS: proprioception

proprioceptors in muscle + inner ear

Sensory Inputs PNS: taste

Taste buds → CN VII, IX, X → thalamus → gustatory cortex

Sensory Inputs PNS: Hearing

→ Ext., int., middle ear →; vestibulocochlear nerve → thalamus → auditory cortex

Sensory Inputs PNS: Balance

Inner ear → thalamus → vestibulo-ocular reflex

Sensory Inputs PNS: Vision

Photoreceptors → CN: II → thalamus → visual cortex

Sensory Inputs PNS: Smell

Olfactory epithelium → CN: I → limbic system

Sensory Inputs CNS (Central Processing) is split into?

Dorsal column and spinothalamic tract

Sensory Inputs CNS: Dorsal column

1. fine touch

2. pressure

3. vibration

*touch → dorsal column

Sensory Inputs CNS: Spinothalamic tract

1. pain

2. temp

Sensory Inputs CNS: Dorsal column pathway

Sensory Inputs CNS: Spinothalamic tract pathway

Face Sensation:

Processed by trigeminothalamic tract, CN X

Face Sensation Pathway

trigeminal ganglion → pons “cross” → thalamus → somatosensory cortex

Thalamus is what?

Main relay station; “switch board”

Somatosensory cortex is what?

Homonuculus “body map”

Order of Nervous System

PNS → CNS → Brain

Brain:

Motor control initiated in frontal lobe

1. prefrontal cortex

   1. executive control (decision making, planning, attention)

2. promotor cortex

   1. posture + simple movement

3. Supplemental motor area

   1. complex + learned movements

4. Broca's area

   1. speech production

5. Primary motor cortex

   1. precentral gyrus → sends to Voluntary muscle movement

6. Primary motor cortex = humonuculus; “map”

   1. larger cortical area given to fingers + face = fine motor control

Motor Output ← (Efferent Exits Brains) ← descending motor pathway (brain → spinal cord → muscles)

-Upper motor neurons = primary motor cortex

Lower motor neurons = start in brainstem or spinal cord and directly stimulate muscle (reflexes) = do not require conscious brain processing

Upper motor neuron tracts

1. Corticobulbar → primary motor cortex → CN → face, head, neck, muscles

Corticospinal

1. Lateral corticospinal

   1. cross at medulla

   2. appendicular muscles

      1. (fine motor movement)

2. Anterior corticospinal

   1. cross at spinal cord

   2. axial muscles

   3. bilateral for posture + locomotion

What does cerebellum do?

Cerebellum compares motor commands from the brain with positions of proprioceptors and makes adjustments accordingly → rubrospinal tract

Balance + posture =

vestibulospinal tract

somatic pathway:

PNS → Dorsal Root → CNS (hypothalamus) → Single motor unit (ventral root) → skeletal muscle

Autonomic nervous system

PNS → Dorsal Root → CNS (hypothalamus) → preganglionic neurons → ganglion → postganglionic neuron → cell body in CNS → axon → cell body in ganglion → target organ

The Autonomic Nervous System regulates involuntary physiological processes necessary

1. for maintaining homeostasis

2. The ANS regulates smooth muscle, cardiac muscle and glands

3. Two main divisions:

   1. Sympathetic = fight or flight

   2. parasympathetic = rest + digest

      1. Target organs of the ANS have dual innervation (sympathetic + parasympathetic)

Sympathetic Division (Thoracolumbar System) T1-L2 Pathway

CNS → Preganglionic Neurons (*lateral horn of spinal cord (short)) → sympathetic ganglion “sympathetic trunk” (paravertebral ganglion) → Postganglionic neuron (long) → target organ

*Preganglionic neurons may what?

Influence 10-20 target organs

Exception of Preganglionic neurons =

1. Adrenal medulla (kidneys)

   1. Produce: epinephrine/norepinephrine

      1. directly innervated by a preganglionic neuron

Parasympathetic Divison

1. Originates in brainstem + S2 - S4 (Sacrum) “Cranio-sacral outflow”

Parasympathetic Divison Pathway

Preganglionic neurons (long) → parasympathetic ganglion (located near target organ) → postganglionic neuron (short)

*parasympathetic response = more localized specific

primary neurotransmitters of ANS

1. Cholinergic (ACETYLCHOLINE)

   1. nicotinic

   2. muscarinic

      1. Adrenergic System (epinephrine/norepinephrine)

         1. alpha/beta receptors

Hypothalamus primary control center of ANS

Coordinates autonomic + endocrine responses

Autonomic nervous system and visceral reflexes

1. regulate internal homeostasis (smooth muscle, cardiac muscle + glands)

Autonomic nervous system and visceral reflexes Pathway

CNS → Preganglion → autonomic ganglion →postganglionic → organ

EX. Baroreceptors = detect blood pressure change

Embryology of Nervous System:

1. Ectoderm → Neural tube

2. Neural Tube

   1. Anterior - brain

   2. posterior - spinal cord

3. Formed around day 25

Embryology of Nervous System: Parts of Ant-Brain

1. forebrain → cerebrum

2. midbrain

3. hindbrain → pons/cerebellum/medulla

Embryology of Nervous System: Parts of post-spinal cord

Dorsal cells = sensory

ventral cells = motor

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE: (Somatic Reflex) Ex. Touching a HOT stove

Sensory Input → (arrives at dorsal root)→ Integration → Motor Output

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Sensory Input: Stimulus

Heat/Pain from hot stove

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Sensory Input: Receptors

Thermoreceptors + nociceptors in skin

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Sensory Input: Neuron

sensory (Afferent) neuron (arrives at brain)

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Integration

*Occurs in spinal cord

Sensory Input: Neuron → Sensory nerve synapses with interneuron “remove hand now”

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Motor Output

1. Neuron = somatic motor neuron

   1. → effector response

      1. target = skeletal muscle

      2. NT= acetylcholine

      3. Effect = NMJ muscle contracts

         1. → hand withdraws

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Stepping on a sharp tack; Sensory Input: Stimulus

Sharp tack in foot

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Sensory Input: Receptors

Nociceptors in skin

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Sensory Input: Activates

Sensory neuron

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Sensory Input → (Pain = spinothalamic tract) → Integration

1. Enters at dorsal horn

2. Crosses at spinal cord

3. Lateral spinothalamic tract to thalamus

   1. Primary somatosensory cortex

      1. Premotor cortex

REVIEW OF SOMATIC NERVOUS SYSTEM RESPONSE;l (Somatic Reflex) Ex. Touching a HOT stove; Motor Response

1. Leaves via ventral horn

   1. (premotorcortex → *Corticospinal tract → leaves via ventral horn)

1. Somatic motor neuron triggers skeletal muscle