Chapter Five - Brachial plexus & muscles in the arm that move the forearm Flashcards
What are the important contents of the axilla (armpit)?
Axilla (armpit) Important contents of the axilla:
- nerves (Brachial plexus)
- vessels (branches of axillary artery and vein)
• lymph nodes
Describe the anatomy of the neuron, and why some parts of the CNS appear white vs gray. What increases the speed of an electrical signal?
Dendrites
Cell body
Axon
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.
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.
Give the three types of neurons based of their function. What do they do?
Functional classification of neurons is based on the direction in which neurons transmit nerve impulses:
- Sensory neurons (afferent neurons) transmit nerve impulses from receptors on the periphery of the body to the central nervous system (CNS).
- Motor neurons (efferent neurons) transmit nerve impulses from the CNS to effectors (muscles, glands).
- Interneurons are neither sensory nor motor neurons; most neurons are of this type.
What is a nerve fibre? What does it contain? What is a nerve bundle?
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.
What is a synapse? What is a ganglion?
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.
Name the two main nervous system divisions, and their two structural components each.
Nervous system divisions:
A. Central nervous system (CNS) consists of:
- Brain
- Spinal cord
B. Peripheral nervous system (PNS) consists of:
- Cranial nerves that emerge from the brain,
- Spinal nerves that emerge from spinal cord.
The PNS is divided into two big subdivisions. What are they, and what components do they each have?
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.
- 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. (Smooth muscles need sympathetic innervation (everywhere in the body), very important because we have arteries everywhere)
Note: no parasympathetics in the extremities or body wall!
Describe the anatomy of a spinal nerve. What does the dorsal root contain? And the ventral root? What is a ramus?
Anatomy of the spinal nerve
Posterior (dorsal) root: sensory fibers only
Anterior (ventral) root: motor fibers only
Spinal nerve is a mixed nerve, i.e., it contains both sensory and motor fibres.
Each spinal nerve gives anterior (ventral) and posterior (dorsal) ramus. Rami are mixed nerves.
Give the general rule number one (posterior vs anterior rami).
General rule #1:
- Posterior (dorsal) rami of spinal nerves supply intrinsic back muscles and skin on the back. Posterior rami = usually more uneventful
- 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).
What is the brachial plexus? What composes its roots? What are its five terminal branches?
Brachial plexus: nerve supply to the upper limb
5 terminal branches of the brachial plexus:
- Musculocutaneous nerve
- Median nerve
- Ulnar nerve
- Radial nerve
- Axillary nerve
« M » formation = good start point in the lab
Draw the brachial plexus. What are its five categories?
In the upper limb, where does the arm move? The forearm? The hand?
UPPER LIMB:
• Arm
- moves at shoulder joint
• Forearm
- moves at elbow joint
• Hand
- moves at wrist joint
What is the general osteology of the upper limb?
Osteology of the upper limb:
- humerus
- radius
- ulna
• bones in the hand
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 possible movements of the forearm?
At the elbow:
- Flexion
- Extension
Between radius and ulna:
- Pronation
- Supination
What are the muscle compartments of the forearm? What do their muscles do?
Muscle compartments in the arm
Muscles in the same compartment usually have the same function and innervation.
- Anterior arm compartment: Flexors
- Posterior arm compartment: Extensors
Give the general rule number two (rami divisions).
General rule #2:
Posterior divisions of ventral rami supply extensor (posterior) muscles.
Anterior divisions of ventral rami supply flexor (anterior) muscles.
What are the muscles in the arm moving the forearm, in the flexor compartment? What are they innervated by?
Coracobrachialis
Biceps brachii
Brachialis
All muscles in the anterior arm are innervated by the Musculocutaneous nerve (C5, C6, C7).
What are the muscles in the arm moving the forearm, in the extensor compartment? What are they innervated by?
Triceps brachii
Anconeus
All muscles in the posterior arm are innervated by the Radial nerve (C5, C6, C7, C8, T1).
Where does Coracobrachialis cross and what does it do?
- Coracobrachialis
crosses shoulder joint but not elbow joint; flexes arm at shoulder joint.
Where does Biceps brachii cross and what does it do?
- Biceps brachii
has 2 heads: long and short. It crosses both shoulder and elbow joints. Both heads flex and supinate forearm; short head weakly flexes arm at shoulder, and long head stabilizes arm at shoulder joint.
Where does Brachialis cross and what does it do?
- Brachialis
crosses the elbow joint and flexes forearm at elbow.
Give the origin, insertion, action and innervation of the coracobrachialis.
Origin: Coracoid process
Action: Flexes arm, weakly adducts arm
Insertion: Middle third of the medial surface of humerus
Nerve: Musculocutaneous nerve
Give the origin, insertion, action and innervation of the biceps brachii.
Origin:
Long head – supraglenoid tubercle of scapula;
Short head – coracoid process of scapula
Action: Flexes forearm, supinates forearm, weak flexor of arm at shoulder (short head), stabilizes shoulder (long head)
Insertion: radial tuberosity (on the radius) and through bicipital aponeurosis into deep fascia on anteromedial forearm
Nerve: Musculocutaneous nerve
Give the origin, insertion, action and innervation of the brachialis.
Origin: Anterior lower half of humerus
Action: Flexes forearm
Insertion: Ulna (proximal end)
Nerve: Musculocutaneous nerve
