Bio 240 2.1 Spinal Cord and Nerves

Spinal Cord

Structural and functional link between brain and rest of body

• All motor and sensory signals that involve the brain will pass through

• 5 regions

• Begins at end of medulla oblongata

Spinal Reflexes

Sensory and motor signals —→ do not involve the brain

• much faster since brain is not involved

Cervical

Region of spinal cord

• Closest to head

• Houses cervical spinal nerves

Thoracic

Region of spinal cord

• Starting at collarbone and ends at ribs

• Houses thoracic nerves

Lumbar

Region of spinal cord

• End of ribcage to top of hips

• Houses lumbar nerves

Sacral

Region of spinal cord

• Middle of hips to pubic bones

• Houses sacral nerves

Coccygeal

Region of spinal cord

Tailbone

• Houses coccygeal vertebrae

Conus Medullaris

End of spinal cord (inferior)

Rootlets

Merge to form roots

Posterior Root

Branching small nerves that attach to spinal cord

• contain sensory neurons

Posterior Root Ganglion

Involved in reflexes

Has satellite cells

Ganglion: cluster of cell bodies in PNS that process sensory signals

Anterior Root

Closest to chest

Contains motor neurons

Mixed Nerves

All spinal nerves become mixed nerves as you move away from spinal cord

Cauda Equina

Connection of lower body signal nerves to conus medullaris

Connect most lumbar nerves, all sacral and coccygeal nerves to spinal cord

• Nerves are still incased in bone of vertebrae

  • Still have rootlets (posterior and anterior)

Vertebral Column

1st supportive and protective mechanism of spinal cord

• All nerves connect to spinal cord are encased in bone

Many Types of Bone

• cervical

• thoracic

• lumbar

• sacral

• coccygeal

  • labeled similar to spinal nerves but don’t match exactly

Vertebral Canal

Channel that houses spinal cord and cauda equina

Intervertebral Foramen

Small holes in bone where spinal nerves enter/exit the vertebral column

Spinal Cord Meninges

2nd protecting mechanism of the spinal cord

Includes

1.) Pia Mater

2.) Arachnoid Mater

3.) Dura Mater

Epidural Space

Space between dura mater and vertebral bones

• contains large vessles

Dura Mater

Layer closest to bone

Subdural Space

Potential space used for blood drainage if spinal cord is damaged

Arachnoid Mater

Forms arachnoid trabeculae —→ protein network

Subarachnoid Space

Where CSF circulates in spinal cord

Choroid Plexus

Where CSF is made (in the brain)

Pia Mater

Tissue layer that adheres to spinal cord

• contains lots of capillaries

Denticulate Ligaments

Anchoring structures between spinal cord and bone

• holds SC in place

Cerebrospinal Fluid

• Circulate nutrients and remove waste

• Liquid cushion for the spinal cord

• Contained in subarachnoid space

Dermatome Maps

Map of spinal nerves that shows which part of the body each nerve corresponds to

• Helps physicians gain info about organs/spinal nerves

Spinal Plexuses

Individual spinal nerves that interconnect branch to larger regions once you leave the spinal cord

Cervical Plexus

C1-C4

• control neck and upper shoulders

Brachial Plexus

L5-T1

• control arms and hands

Lumber Plexus

L1-L4

• controls upper thighs and abdominal wall

Sacral Plexus

L4-S4

• controls legs and feet

Reflexes

Automatic and preprogrammed response to a stimulus

• most are not a conscious decision (not controlled by brain)

  • rapid responses —→ bypass the brain

Reflex Arc

Arc of sensory and motor neurons involved in or control a reflex

Spinal reflexes

Controlled and sensed by spinal cord and spinal nerves

• 4 types

Cranial Reflexes

Sensed and controlled by cranial nerves

• still automatic and protected response

  • Ex: blinking

Somatic Reflexes

Involving skeletal muscles

Visceral (automatic) Reflexes

Involving cardiac + smooth muscles and glands

Ex: pupillary reflex (protection from UV)

Monosynaptic Reflex

1 sensory neuron and 1 motor neuron —→ 1 synapse

• quick reflex

Polysynaptic Reflex

Involve multiple interneurons —→ multiple synapses

• slower reflex

Ipsilateral

Reflexes correspond to same side of body

Contralateral

Reflexes correspond to opposite side of body

Innate Reflex

Born with that response

Acquired Reflex

Learned reflex

Ex: salivating at favorite food

Proprioceptors

Sensory neuron that detects body positioning and stretching

Muscle Spindle

AKA stretch receptor

Structure found in skeletal muscle that contains proprioceptors in stretch reflex

Intrafusal Muscle Fibers

Muscle spindles that detect stretch

Gamma Motor Neurons

Small neurons that respond to stretching (initiate reflex)

Extrafusal Muscle Fibers

Fibers not within the spindle

Alpha Motor Neurons

Control extrafusal muscles

• large diametere

Stretch Refkex

Type of spinal reflex

Somatic, spinal, ipsilateral, polysynaptic, monosynaptic movement

Reflexive response to muscle stretching —> cause a contraction

Muscle Spindle Proprioceptor

Detect stretch in whole muscle

Gamma Motor Neurons

Reflexive contraction of that same muscle

• Regulates muscle spindles sensitivity

  • Monosynaptic response

Reciprocal Inhibition

Reflexive force in where agonist muscle is activated while antagonist muscle is inhibited

Golgi Tendon Reflex

Type of spinal reflex

Reflexive inhibition or relaxation of muscles after contractions

Tendon Organs

Neurons at muscular-tendon section

• detecting excessive muscular contraction

Reciprocal Activation

When interneurons excite motor neurons of antagonist muscle

• relives tension

Flexor Reflex (withdrawal)

Type of spinal reflex

Reflexive response to pain (pull away from the source of damage)

• Detected by nociceptors (pain receptors)

• Polysynaptic, ipsilateral, innate reflex

Contraction of Flexor Muscles —> hamstring

Inhibition of Extensor Muscles —→ quadricep

Crossed-Extensor Reflex

Occurs at the same time as the withdrawal reflex

Reflexive contraction of muscles on the opposite side of the body (helps keep balance)

• Contralateral type reflex