Neurons, the Spinal Cord, and Spinal Nerves

Chapter 19

What are the three major parts of a motor neuron?

• The soma

• Dendrites

• Axon

Soma

Highlighted in blue

Dendrites

Highlighted in purple

Axon

Highlighted in red

What are the major structures of the soma?

• The nucleus

• Nissl bodies

Nucleus

Highlighted in blue

Nissl body

Highlighted in purple

Dendrites

Emanate from the soma

Telodendria

Highlighted in blue. They attach (synapse) their axon terminals onto dendrites and soma

Axon terminals

Highlighted in purple

Axon hilock

Emanates from the soma, just before the axon

Axolemma

Cell membrane of the axon

Neurolemmocytes (Schwann cells)

Makes myelin sheaths for axons in the PNS

Nodes of Ranvier

Gap between schwann cells that allow for messages to travel faster down the axon

Neurilemma

Plasma membrane of a neurolemmocyte

Endoneurium

Loose connective tissue that covers the neurolemmocytes

Anterior median fissure

Highlighted in blue

What are the regions of the spinal cord?

1. Cervical

2. Thoracic

3. Lumber

4. Sacral

5. Coccygeal

Cervical spinal cord

Cervical enlargement of the spinal cord

A thickened portion of the spinal cord; due to many motor and sensory neurons that serve the upper limbs

What is a plexus?

A network of intersecting nerves, blood vessels, or lymphatic vessels in the body

Cervical plexus

Network of nerves formed by the anterior rami of spinal nerves C1-C4. Supplies nerves for the back of your head and the upper cervical muscles

Phrenic nerve

Emanates from the cervical plexus and takes motor signal to the diaphragm

Brachial plexus

Network of nerves formed by the anterior rami of spinal nerves C5-T1. Serves your chest, shoulder, and arms

Thoracic spinal cord

Highlighted in blue. Sits alongside the ribcage

Lumbar region of the spinal cord

Highlighted in blue

Sacral region of the spinal cord

Highlighted in red

Coccygeal region of the spinal cord

Highlighted in purple

Lumbosacral enlargement of the spinal cord

Thickened area that contains numerous motor and sensory neurons serving the lower limbs

Conus medullaris

Tapered inferior portion of the spinal cord. Found generally at the L1 vertebra

Filum terminale

A strand of pia mater that anchors the conus medullaris to the posterior coccyx

Cauda equina

Collection of lumbar and sacral spinal nerves running through the vertebral canal

Lumbosacral plexus

Network of nerves formed by the anterior rami of spinal nerves

Obturator nerve

Takes motor and sensory signal to/from the medial thigh

Sciatic nerve

Take motor signals to the hamstring muscles and carries sensory information from most of the posterior thigh, leg, and foot

Spinal dura mater

Arachnoid mater

Subarachnoid space

Continuous with the 4th ventricle and contains CSF

Pia mater

Actually surrounds the spinal cord

Posterior median sulcus

Posterior funiculus

White matter region of the spinal cord located on the dorsal side. Conveys information on touch and proprioception

Lateral funiculus

White matter region. Provides sensory signals to the cerebellum and thalamus and motor commands from the cortex and brainstem

Anterior funiculus

Provide sensory signals to the thalamus as well as motor commands involved in balance and coordination

Anterior median fissure

Ventral horn of the spinal cord

Contains cell bodies of somatic motor neurons. Their axons will travel to skeletal muscles

Dorsal horn of the spinal cord

Contains axons from sensory neurons. Provides information from the body regarding touch and proprioception

Grey commissure

Connects the 2 halves of the spinal grey matter

Central canal of the spinal cord

Contains CSF and is continuous with the 4th ventricle

Dorsal root

Contains sensory axons bringing sensory information into the dorsal horn

Dorsal root ganglion

Contains cell bodies of the sensory neurons bringing sensory information into the spinal cord

Ventral root

Contains the axons of the ventral horn motor neurons that will travel to skeletal muscles

Spinal nerve

Contains sensory axons of the dorsal root and the motor axons of the ventral root and is therefore considered a mixed nerve

Lateral horn

• Only found in the thoracic and upper lumbar parts of the spinal cord

• Contain cell bodies of autonomic motor neurons that send axons from the ventral root to synapse with smooth muscle, cardiac muscle, and glands

Spinal nerve

What is the blue arrow

posterior ramus

What is the red arrow

anterior ramus

What kin of neurons are in this image?

multipolor motor meurons