Spinal cord, pns, synapses

spinal cord anatomy

extends from foramen magnum to L1/L2

spinal cord enlargments

• cervical

• lumbosacral

gray matter

• dorsal horn

• ventral horn

• lateral horn

white matter

funiculi

anterior ventral roots

• motor efferent

  • skeletal mm

posterior dorsal roots

• sensory afferent

  • receptors

ventral root + dorsal root =

spinal nerve

how many pairs of spinal nerves?

31

C1-C8

cervical nerves

T1-T12

thoracic spinal nerves

L1-L5

lumbar spinal nerve

S1-S5

sacral spinal nerve

Co1

coccygeal

mechanoreceptors

responds to touch, pressure, vibration, stretch, sound waves (mechanical forces)

nociceptors

responds to extreme heat, pressure, or chemical damage (painful stimuli)

thermoreceptors

respond to temperature changes

photoreceptors

respond to light

chemoreceptors

respons to oxygen, carbon dioxide, pH, smell, taste (chemical changes)

exteroceptors

• Location: Near/on the body surface (skin, special sense organs).

• Stimuli detected: External environment.

• Examples:

  • Touch, pressure, pain, and temperature receptors in skin

  • Special sense organs: eyes (photoreceptors), ears (hair cells), nose (olfactory), tongue (taste buds)

interoceptors (visceroceptors)

• Location: In internal organs and blood vessels.

• Stimuli detected: Internal environment.

• Examples:

  • Baroreceptors (blood pressure in carotid sinus, aortic arch)

  • Chemoreceptors (O₂, CO₂, pH in carotid/aortic bodies)

  • Stretch receptors in stomach, bladder, intestines

  • Pain receptors in viscera

proprioceptors

• Location: Muscles, tendons, joints, and inner ear.

• Stimuli detected: Body position, movement, and balance.

• Examples:

  • Muscle spindles (muscle stretch)

  • Golgi tendon organs (tension in tendons)

  • Joint kinesthetic receptors (movement, angle)

  • Vestibular apparatus in inner ear (balance, equilibrium)

exteroceptors=

outside world

interoceptors=

inside body

proprioceptors=

body position and movement

nonencapsulated (free) nerve endings

• Structure: Bare (uncovered) nerve endings or with very little specialization.

• Location: Widely distributed in epithelia and connective tissues.

• Stimuli detected: Pain, temperature, light touch, hair movement.

• Examples:

  • Free nerve endings → pain & temperature (nociceptors, thermoreceptors)

  • Merkel discs (tactile discs) → light touch, pressure (in epidermis)

  • Hair follicle receptors → light touch (movement of hair)

encapsulated nerve endings

• Structure: Nerve endings enclosed in a connective tissue capsule.

• Location: Mostly in skin, muscles, tendons, joints.

• Stimuli detected: Pressure, vibration, stretch, proprioception.

• Examples:

  • Meissner’s (tactile) corpuscles → light touch (in dermal papillae of skin)

  • Pacinian (lamellar) corpuscles → deep pressure & vibration

  • Ruffini endings (bulbous corpuscles) → deep pressure, skin stretch

  • Muscle spindles → muscle stretch (proprioception)

  • Golgi tendon organs → tendon stretch/tension (proprioception)

  • Joint kinesthetic receptors → joint position and movement

brachial plexus

provides virtually al nerves for the upper extremity

where does brachial plexus contribute from?

C5-T1

where does brachail plexus emerge from?

anterior and middle scalene mm.

what makes up brachial plexus

roots, trunks, divisions, cords, branches

terminal branches in brachial plexus

• musculocutaneous n

• axillary n

• radial n

• median n

• ulnar n

lumbar plexus

provides nerves for lower abdomen, anterior and medial thigh

where does lumbar plexus contribute from?

L1-L4

terminal branches of lumbar plexus

• femoral n

• obturator n

sacral plexus

provides nerves for pelvis, posterior thigh, and virtually all of the leg and foot

where does sacral plexus contribute from?

L4-S5

where does sacral plexus emerge from?

pelvis

terminal branches of sacral plexus

• sciatic n

• tibial n

• common fibular n 

• deep fibular n 

• superficial fibular n

synapses

junction that mediates info from one neuro ton another

location of synapses

1. axosomatic

2. axodendritic

3. axoaxonal

types of synapses

• chemical 

• electrical

chemical synapses

utilize neurotransmitters

components of chemical synapses

axon terminal: presynaptic

receptor region: post synaptic

synaptic cleft: gap between axon terminal and receptor region

synaptic delay

rate limiting segment for transmission of information

chemical synapse steps

1. Action potential arrives at presynaptic terminal.

2. Voltage-gated Ca²⁺ channels open, allowing calcium influx.

3. Vesicles fuse with presynaptic membrane (exocytosis).

4. Neurotransmitter diffuses across the synaptic cleft.

5. Neurotransmitter binds to postsynaptic receptors.

6. Ion channels open in postsynaptic membrane → postsynaptic potential

excitatory adrenergic synapse

• the unstimulated NE receptor is bound to a G protein
  2. Binding of NE to the receptor causes the protein to dissociate
  3. The protein binds to adenylate cyclase (enzyme) and activate it, which converts ATP to
  cAMP
  4. Cyclic AMP can induce several alternative effects in the cell*

  • Produce an internal chemical that binds to a ligand-gated ion channel, opening the channel and depolarizing the cell

  • Activate preexisting cytoplasmic enzymes, which lead to metabolic changes

  • CAMP to induce genetic transcription, so new enzymes are produced that lead to
    metabolic effects

postsynaptic potential-excitatory

neurotransmitter binding results in depolarization of the postsynaptic membrane

epsp

excitatory postsynaptic potential

goal on an epsp?

help trigger an AP distally at the neurons axon

postsynaptic potential- inhibatory

neurotransmitter binding results in hyperpolarization of the postsynaptic membrane

ipsp

inhibitory postsynaptic potential

goal on an ipsp

create a more negative membrane

what is a plexus

collection of spinal nerves

are chemical or electrical synapses more common

chemical

why are epsp and ipsps different from aps

they are small, local variable changes while aps are large all or none spikes