The Spinal Cord

cranial nerves- 12 pr

spinal nerves- 31 pr

The Spinal Cord

ventral root

pia mater

dura mater

arachnoid

grey matter

dorsal root

white matter

spinal nerves

The Spinal Cord

spinal cord

spinal nerve

vertebra

Nerve Pathways into the Spinal Cord sensory

pathway

motor pathway

Neuron-To-Neuron Transmission

synapses

Cervical Plexus

• Formed by ventral rami of C1–C4

• Innervates skin and muscles of the neck, ear, back of head, and shoulders

• Phrenic nerve– Major motor and sensory nerve of the

diaphragm (receives fibers from C3–C5)

Brachial Plexus

• Formed by ventral rami of C5–C8 and T1 (and often C4 and T2)

• It gives rise to the nerves that innervate the upper limb

• Major branches of this plexus: – Roots—five ventral rami (C5–T1)– Trunks—upper, middle, and lower– Divisions—anterior and posterior – Cords—lateral, medial, and posterior

Figure 13.9 (a)

Upper

Middle Trunks

Lower

Roots (ventral rami):

Upper subscapularLower subscapularThoracodorsalMedial cutaneousnerves of the armand forearm

Long thoracicMedial pectoralLateral pectoral

Nerve tosubclaviusSuprascapular

Dorsal scapular

Posteriordivisions

Anteriordivisions

Lateral

PosteriorCords

Medial

AxillaryMusculo-cutaneousRadialMedianUlnar

Posteriordivisions

Trunks Roots

C4

C5

C6

C7

C8

T1

(a) Roots (rami C5 – T1), trunks, divisions, and cords

Brachial Plexus: Nerves• Axillary—innervates the deltoid, teres minor, and skin

and joint capsule of the shoulder• Musculocutaneous—innervates the biceps brachii and

brachialis and skin of lateral forearm• Median—innervates the skin, most flexors and pronators

in the forearm, and some intrinsic muscles of the hand• Ulnar—supplies the flexor carpi ulnaris, part of the flexor

digitorum profundus, most intrinsic muscles of the hand, and skin of medial aspect of hand

• Radial—innervates essentially all extensor muscles, supinators, and posterior skin of limb

Figure 13.9 (c)

Median nerve

Musculocutaneous nerveRadial nerveHumerus

Ulna

Ulnar nerveMedian nerve

Radius

Radial nerve (superficial branch)

Superficial branch of ulnar nerveDorsal branch of ulnar nerve

Digital branch of ulnar nerveMuscular branchDigital branch

(c) The major nerves of the upper limb

Axillarynerve

Anteriordivisions

Posteriordivisions

Trunks Roots

• T3-T12• 11 intercostal nerve• 1 subcostal nerve

Lumbar Plexus

• Arises from L1–L4

• Innervates the thigh, abdominal wall, and psoas muscle

• Femoral nerve—innervates quadriceps and skin of anterior thigh and medial surface of leg

• Obturator nerve—passes through obturator foramen to innervate adductor muscles

Sacral Plexus

• Arises from L4–S4

• Serves the buttock, lower limb, pelvic structures, and perineum

• Sciatic nerve– Longest and thickest nerve of the body– Innervates the hamstring muscles, adductor

magnus, and most muscles in the leg and foot– Composed of two nerves: tibial and common

fibular

Functional Divisions of the Peripheral Nervous System

Afferent Division– Sensory (advances) neuron –

goes toward CNSEfferent Division

– Motor (exits) neuron- leaves CNS– Somatic Nervous System– Autonomic Nervous System

Spinal Reflex Arc

patellar ligament

stretch receptor

motor neuron

sensory neuron

motor neuron

interneuron

Figure 13.18, step 1

+ Excitatory synapse– Inhibitory synapse

Quadriceps strongly contracts. Golgi tendon organs are activated.

Interneurons

Spinal cord

Quadriceps(extensors)

Golgitendon

organHamstrings

(flexors)

1

Figure 13.18, step 2

+ Excitatory synapse– Inhibitory synapse

Quadriceps strongly contracts. Golgi tendon organs are activated.

Afferent fibers synapse with interneurons in the spinal cord.

Interneurons

Spinal cord

Quadriceps(extensors)

Golgitendon

organHamstrings

(flexors)

1 2

Figure 13.18, step 3a

+ Excitatory synapse– Inhibitory synapse

Quadriceps strongly contracts. Golgi tendon organs are activated.

Afferent fibers synapse with interneurons in the spinal cord.

Efferent impulses to muscle with stretched tendon are damped. Muscle relaxes, reducing tension.

Interneurons

Spinal cord

Quadriceps(extensors)

Golgitendon

organHamstrings

(flexors)

1 2

3a

Figure 13.18, step 3b

+ Excitatory synapse– Inhibitory synapse

Quadriceps strongly contracts. Golgi tendon organs are activated.

Afferent fibers synapse with interneurons in the spinal cord.

Efferent impulses to muscle with stretched tendon are damped. Muscle relaxes, reducing tension.

Efferent impulses to antagonist muscle cause it to contract.

Interneurons

Spinal cord

Quadriceps(extensors)

Golgitendon

organHamstrings

(flexors)

1 2

3a 3b

Reflex Arc

1. Sensory receptor2. Sensory neuron3. Integration center4. Motor neuron5. Effector- part of body that

responds to a motor nerve impulse

INQUIRY

1. What is a reflex?2. Damage of the spinal cord

above C3 can result in_____?

3. In which portion of the spinal cord do the interneurons lie?

4. What kind of peripheral nerve fiber carries motor impulses outward to smooth muscles and glands of internal organs?