Neural Flashcards
What does the Somatic Motor System do?
Provides conscious, voluntary control over skeletal muscles.
Motor commands are issued by the primary cortex in response to conscious decision to make a specific movement
Primary Motor cortex. (M1)
Pyramidal cells from layer of the cerebral cortex synapse with the brainstem or spinal cord.
Regions of the primary motor cortex map to regions of the body and this be represented as a motor homunculus
Greater control required - larger area assigned of M1
Motor pathways in the CNS and PNS
Upper motor neuron - cranial nerve nuclei / somatic motor nuclei of brainstem-> skeletal muscle of face, hand and neck
Lower motor nuclei - somatic motor nuclei of spinal cord -> skeletal muscle of lower body
Upper limbs
- pyramids to lateral corticospinal tract
Decussation of Lateral corticospinal tract
85% of UMN - controlling more distal muscles - e.g hand
Decussation of Anterior corticospinal tract
15% - control more proximal or axial muscles
Proprioceptors
Sense of where our muscles are in space
Golgi tendon organ
sensing tension - prevent damage
Muscle spindle afferents
Control muscle length
Muscle spindle afferents of lower body pathway
To Clarke’s’ nucleus to dorsal spinocerebellar tract to cerebellum and dorsal column nuclei
Muscle spindle afferents, upper body pathway
Straight to cerebellum and dorsal column nuclei
Somatosensory system
Receptors in our skin
Have different structures and location
Merkel cells
Fine touch and detail
Free nerve ending
light, pain, temperature
Tactile corpuscle
vibration
Ruffini corpuscle
Pressure
Lamellated corpuscle
Vibration
Exteroreceptors, proprioceptors of back, body wall and limbs
From dorsal and ventral ramus respectively and travel to the somatic sensory area
Interoceptors
Travel to the visceral sensory area
Posterior-column pathway function
carries proprioception, fine touch, pressure and vibration
Anterior spinothalamic tract function
carries crude touch and pressure sensations
Lateral spinothalamic tract function
carries pain and temperature sensations
Sensory modality arrangement
Fine touch, pressure, vibration, pain and temp, crude touch
Somatotopic arrangement
Different info from different sources is carried in different parts
Medial-lateral rule
Leg in middle
Arm on outside
In terms of spinal cord
Medial lemniscus pathway
Axons of first order neurons enter spinal cord through dorsal root and ascend the fasciculus cuneatus or grailus
Fasciculus cuneatus
upper body
Fasciculus gracilus
lower body
Nucleus cuneatus and gracilus
Second order neurons that synapse in the thalamus. Axons decussate here
Medial lemniscus
carries axons and synapses in the ventral posterolateral nucleus (VPN) of the thalamus to third order neurons
Reflex arc
allows for immediate involuntary response to stimuli
Monosynaptic
Involves a peripheral sensory neuron and a central motor neuron. Stimulation will lead to a reflexive contraction in a skeletal muscle
Polysynaptic
Polysynaptic reflex circuit involves a sensory neuron, interneurons and motor neurons.
Stimulation of receptor leads to coordinated contractions of two different skeletal muscles
Nerve plexuses
Adjacent spinal nerves blend their fibres to produce a series of compound nerve trunks. This interwoven network of nerves is a called a nerve plexus
Four nerve plexus
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Brachial plexus
C5-T1
Innervates the upper limb
The root emerging from C5-T1 unite to form the superior, middle and inferior trunks and they divide into posterior and anterior division
Lateral cord
Anterior divisions of superior and middle trunk
Posterior cord
Posterior division of all three trunks
Medial cord
Anterior division of the inferior trunk
Nerves of the arm and forearm
Musculocutaneous nerve, radial nerve, median nerve and ulnar nerve
Musculocutaneous nerve
Innervates muscles of the anterior arm. Lateral cutaneous nerve of the forearm - lateral aspect of forearm
Nerve roots C5-7
Radial nerve
Innervates muscles of the posterior arm and posterior compartment of the forearm
Nerve roots C5-T1
Lower lateral cutaneous nerve of arm
Innervates the lateral aspect of the upper arm, below the delts
C5-C6
Posterior cutaneous nerve of arm
Innervates the posterior surface of the upper arm
C6-C8
Posterior cutaneous nerve of forearm
Innervates a strip of skin down the middle of the posterior forearm
C6-C8
Superficial branch of radial nerve
Innervates the dorsal surface of the hand and lateral 3 and half digits and dorsum of thumb
C7-C8
Median nerve
Innervates muscles of the anterior (flexor) compartment of the forearm. Thenar muscles of the hand and first two lumbricals
Nerve roots C6-T1
Palmar cutaneous branch of radial
Innervates lateral aspect of palm
Palmar digital cutaneous branch of radial
Innervates the palmar surface and fingertips of the lateral three and half digits
Ulnar nerve
Innervates two muscles of the anterior compartment of the forearm: flexor digitorum profundus and flexor carpi ulnaris
Nerve roots: C8-T1
Palmar cutaneous branch of ulnar
Innervates the skin of the medial half of the palm
Dorsal cutaneous branch of ulnar
Innervates skin of dorsal surface of medial aspect of the hand and medial one and half fingers
Superficial branch of ulnar
Innervates the palmar surface of the medial one and a half fingers
Axillary Nerve
Gives of superior lateral cutaneous nerve of the arm, which innervates the inferior region of the deltoid. C5-C6
Deltoids, teres major
Medial brachial cutaneous nerve from medial cord
Innervates medial surface of upper arm
Medial antebrachial cutaneous nerve of medial cord
Innervates anterior surface of the arm and medial surface of the lower arm
Brachial plexus injury
Traumatic injury that involves damage to the shoulder or arm can cause damage to the brachial plexus
Erbs palsy
C5-C6 superior trunk
Musculocutaneous and axillary nerve
Loss of function of shoulder and upper arm - usually permanent -> muscle wasting of upper arm
Klumpke’s Palsy
C8-T1 inferior trunk
Loss of function of the lower arm, wrist and fingers
Musculocutaneous nerve injury
Flexion of the shoulder and elbow and supination of forearm are weakened
Pec and brachioradialis unaffected
Loss of sensation (lateral aspect)
Radial nerve injury - In Axilla
Loss of function of all muscles innervated by radial nerve. Wrist drop
Loss of sensation
Radial nerve injury - in radial groove
Weakening of triceps, loss of function of muscles in posterior forearm.
Some innervation of triceps above radial groove
Radial nerve injury in forearm - Deep branch (posterior interosseous nerve)
Majority of muscles in posterior forearm are affected. Wrist drop doesn’t occur. Some innervation occurs at top of forearm.
Radial nerve injury in forearm - Superficial branch
Loss of sensation of dorsal three and half of digits
Median nerve injury
Damage at elbow, pronation of forearm affected, weak flexion of the wrist, opposition of thumb and flexion of first two fingers affected.
Damage at wrist - Thenar muscles and lateral two lumbricals. Opposition of thumb and flexion of first two fingers affected
Median nerve injury - carpal tunnel syndrome
Caused by nerve being trapped in carpal tunnel
Leads to numbness of areas of hand innervated by median nerve
Get thenar wasting
Ulnar nerve injury
Damage to medial epicondyle, flexion of wrist can still occur but is accompanied by abduction
Get impairment of muscles of the hand innervated by ulnar nerve. Finger ab/adduction affection with flex/extension of index and ring finger
Loss of sensation from medial aspect of hand and fingers.
