Lecture 6 - Brachial plexus; Muscles in the arm that move the forearm Flashcards
What are the important contents of the axilla?
- nerves (Brachial plexus)
- vessels (branches of axillary artery and vein)
- lymph nodes
What is a neuron?
Neurons range in length from
less than 1 mm to greater than
1 meter, and transmit nerve
impulses at speeds from 0.5 to
130 m/s.
Most axons are myelinated, i.e., surrounded by a myelin sheath (white); myelin insulates
and protects axons to increase the speed of electrical signal along the axon.
What is the difference between white matter and gray matter?
Some regions in the central nervous system (CNS) appear white and others appear gray:
white matter contains axons (neuronal processes that have myelin).
gray matter contains mainly neuronal cell bodies and dendrites.
What is the functional classification of neurons?
Functional classification of neurons is based on the direction in which neurons transmit
nerve impulses:
1. Sensory neurons (afferent neurons) transmit nerve impulses from receptors on the
periphery of the body to the central nervous system (CNS).
2. Motor neurons (efferent neurons) transmit nerve impulses from the CNS to effectors
(muscles, glands).
3. Interneurons are neither sensory nor motor neurons; most neurons are of this type
Define these terms:
Nerve fibre
Nerve
Synapse
Ganglion
Nerve fibre
is a general term for any neuronal process (dendrite or axon) but usually refers to an axon.
Nerve is a bundle of many nerve fibres.
Most nerves contain both sensory and motor fibres and are surrounded by connective
tissue coat.
Synapse is the junction between two neurons, or between a neuron and an effector
(muscle or gland) cell.
Ganglion is a collection of neuronal bodies.
How is the nervous system divided?
Nervous system divisions:
A. Central nervous system (CNS) consists of:
1. Brain
2. Spinal cord
B. Peripheral nervous system (PNS) consists of:
1. Cranial nerves that emerge from the brain,
2. Spinal nerves that emerge from spinal cord.
What are the two major subdivisions for PNS?
PNS is divided into two major subdivisions:
1. SOMATIC nervous system (voluntary) consisting of:
• sensory neurons that transmit information from cutaneous (skin) and special sense
receptors to CNS, and
• motor neurons that transmit messages from CNS to skeletal muscles.
2. AUTONOMIC nervous system (involuntary) consisting of:
• sensory neurons that transmit information from visceral receptors to the CNS,
• motor neurons that transmit messages from CNS to smooth muscle, cardiac muscle
and glands.
Motor portion of the ANS consists of sympathetic and parasympathetic division.
Note: no parasympathetics in the extremities or body wall!
Anatomy of the spinal nerve
Explain
+ fill in the blanks
Spinal nerve is a mixed nerve, i.e., it contains both sensory and motor fibres.
Posterior (dorsal) root
Anterior (ventral) root
Each spinal nerve gives anterior (ventral) and posterior (dorsal) ramus. Rami are
mixed nerves
What is the general rule #1 about the nerves? What do they supply?
• Posterior (dorsal) rami of spinal nerves supply intrinsic back muscles and skin on
the back.
• Anterior (ventral) rami of spinal nerves supply “everything else”, i.e., all muscles
anterior to transverse processes of vertebrae, and most muscles attaching scapula
and humerus to axial skeleton (e.g., levator scapulae, rhomboids, latissimus dorsi).
Identify this image
Brachial plexus: nerve supply to the upper limb
What are the 5 terminal branches of the brachial plexus?
- Musculocutaneous nerve
- Median nerve
- Ulnar nerve
- Radial nerve
- Axillary nerve
Draw the different components of the brachial plexus.
What composes the upper limb? (general idea)
What is the only bony connection of the upper limb to the trunk?
• Arm
- moves at shoulder joint
• Forearm
- moves at elbow joint
• Hand
- moves at wrist joint
Note: The only bony connection of the
upper limb (appendicular skeleton) to
the trunk (axial skeleton) is the
clavicle. All other attachments are
muscular.
What are the different movements of the forearm?
Muscle compartments in the arm
Muscles in the same compartment usually have the same function and
innervation.
1. Anterior arm compartment: Flexors
2. Posterior arm compartment: Extensors
Identify this image
Coracobrachialis
Biceps brachii
Brachialis
Brachioradialis
What are the extensor (posterior) compartment of the arm?
The principal muscle in the posterior arm is Triceps brachii.
1. Triceps brachii
has 3 heads; crosses both shoulder (long head) and elbow (all heads) joints;
only the long head extends the arm at the shoulder joint, while all three
heads extend the forearm at the elbow.
Triceps brachii
Sensory (cutaneous, i.e., skin) innervation of the upper limb
Areas of skin of the upper limb are innervated by various cutaneous nerves from the
brachial plexus. Each cutaneous nerve may carry fibers to two or more spinal nerves.
S
What are dermatomes?
Identify the different dermatomes on your body.
Dermatomes
Dermatomes are strips, or
areas, of skin innervated by a
single spinal nerve, i.e., the
sensory information from a
dermatome is going to a single
spinal nerve.
A dermatome is tested for
sensation at a point as far away
from other dermatomes as
possible to reduce the possibility
of overlap with adjacent
dermatomes.
Blood supply of the upper limb
Subclavian artery à Axillary artery à Brachial artery à
Radial and Ulnar arteries à Superficial and Deep palmar arch
