Peripheral nervous system
Nervous system organisation
- The Peripheral nervous system splits into the autonomic nervous system and somatic nervous system.
- The autonomic nervous system then controls: sympathetic, parasympathetic and enteric nervous system.
- Somatic nervous system, supplies motor fibres to skeletal muscle and sensory fibres from the skin, skeletal muscles and joints (cranial nerves).
Spinal nerves
- Is a tubular bundle of nervous and connective tissue and is a continuation of the medulla obligate through the foramen magnums and ends at the level of L1/ L2 with the conus medullaris.
- The spinal cord has one of two an enlargement at C4 – T1 as this area is involved in the innovation of the upper limbs.
- The spinal cord also has an enlargement at the lever of T11-L1 as this area is involved in the innovation of the lower limb.
- There are 31 paired spinal nerves, these are made up of Dorsal roots which is sensory, and ventral roots which involved in motor control. These join together to form a single spinal nerve. They leave the vertebral canal via the intervertebral foramina dividing into:
o small posterior rami, innervates deep muscle of back and overlaying skin
o large anterior rami, innervates most other skeletal muscles, and the remaining skin (except head).
- Areas of spinal cord are divided into specific areas depending on which spinal vertebrae they are next to:
o Cervical nerves are C1- C8
o Thoracic nerves are T1 – T12
o Lumbar nerves are L1 – L5
o Sacral S1- S5
o Coccygeal nerve Co.
- The spinal roots become much longer for lower regions
- The spinal nerves are named buy the vertebrae they leave under
Nerve plexus
- This is when your peripheral nerves dived and join with other peripheral nerves to form a network, this permits the individual nerve fibres to pass from one peripheral nerve to another allowing redistribution of nerves.
- Peripheral nerve, is a bundle of nerve fibres in a sheath and can be cranial or spinal.
- Ganglion, is the collection of nerve bodies outside of the CNS.
- It Is combining of nerves from different sources or levels, can form new nerves with specific targets such as: Somatic, Autonomic.
- Cervical plexus, this is from the anterior rami of C1 – C4 and is located on the posterior triangle of the neck. There are numerous branches:
o Motor branches, support movement of head and neck and strap muscles assist swallowing.
o Sensory branches, provide sensory innervation for the inferior parts of head, neck and upper anterior thoracic wall.
The Phrenic nerve is a major branch of the Cervical plexus and its roots are from the anterior rami of the C3 – C5, it travels down the surface of anterior scalene muscle and descends through the thorax on either side. It is responsible for the motor innervation to the diaphragm which is virtual during respiration and also carries sensory information from the pleura and pericardium.
- Brachial plexus, is formed from the anterior rami of C5 – T1 and is located on the root of the neck towards the axilla. It innervates the skin and musculature of the upper limb. At the neck base the roots of the brachial plexus converge forming 3 trunks:
o Superior trunk, which is made up of C5 and C6 nerve roots
o Middle trunk, which is made up of the C7 nerve root
o Inferior trunk, which is made up of the C8 and T1 nerve roots
These trunks divide anteriorly and posteriorly to give rise to cords and further the main branches of the brachial plexus, with the 5 major terminal branches being:
o Axillary nerve, this made up by the C5 and C6 nerve roots. It innervates the deltoid and teres minor muscle and so helps with abduction at the shoulder joint. It also supplies sensory innervation to the regimental badge region and a common condition associated with damage to this branch is Erb’s palsy.
o Musculocutaneous nerve, is made up of the C5, C6 and C7 nerve roots. It innervates the: biceps brachi, brachialis and Coracobrachialis and so helps with flexion at elbow joint. It also supplies sensory innervation to the lateral forearm, and so damage to this nerve leads loss of sensation in the lateral side of the forearm.
o Median nerve, is made up of the C6, C7, C8 and T1 nerve roots. It innervates: palman’s longus, flexor carpi radials, pronator teres, flexor digitorum (superficialis and profundus). It also supplies sensory innervation to the lateral palm and lateral 3 ½ fingers, damage is associated with carpel tunnel syndrome (tigering in first 3 ½ fingers) and also benedict’s hand.
o Radial nerve, is made up of the C5, C6, C7, C8 and T1nerve roots. It innervates: triceps brachii, wrist and fingers extensors, wrist and elbow extension. It also supplies sensory innervation to the posterior arm and forearm, and postero-lateral hand with a common disorder associated being wrist drop.
o Ulnar nerve, is made up of C8 and T1nerve roots. It innervates flexor carpi ulnaris for wrist flexion. It also supplies sensory innervation to the medial palm and 1 ½ digits, damage can lead to loss of sensation in ring and little finger.
- Intercostal nerves, these lie in the intercostal spaces between adjacent ribs and pass laterally around the thoracic wall. The roots of the nerves are from the anterior rami of T2 – T11. There is also the subcostal nerve T12 which runs inferior to rib 12.
- Lumbar plexus, is formed from the anterior rami of T12 – L5 and is located on the lumbar region. It innervates the skin and musculature of lower limbs. And these nerve roots branch into 6 major terminal branches:
o Femoral nerve, is made up of L2, L3 and L4 nerve roots. It innervates: Iliacus, pectineus, sartorius and quadriceps femoris. It also supplies sensory innervation to the skin of anterior thigh and medial surface of leg.
o Obturator nerve, is made up of L2, L3 and L4 nerve roots. It innervates: obturator externus, pectineus and medial thigh. It also supplies sensory innervation to the skin of the medial thigh.
o Lateral cutaneous nerve of thigh
o Genitofemoral nerve
o Ilio-inguinal nerve
o Iliohypogastric nerve
- Sacral plexus, is formed from the anterior rami of L4 – S4 and is located on the posterior pelvic wall. It innervates the skin, muscles of pelvis and lower limb. It then ends in 5 major terminal branches:
o Superior gluteal nerve, is made up of the L4, L5 and S1 nerve roots. It innervates the: gluteus Medius and minimus, and tensor fasciae latae. It does not have any role in sensory innovation.
o Inferior gluteal nerve, is made up of the L4, S1 and S2 nerve roots. It innervates the gluteus maximus but does not play a role in sensory innovation.
o Sciatic nerve, is made up of the L4, L5, S1, S2 and S3 nerve roots. It is also the largest nerve in the body being about 2cm wide. This nerve then further branches in to:
§ Tibial nerve, this provides innervation to hamstrings, posterior leg and the sole of the foot. It also provides sensory innovation to the lateral and sole of the foot.
§ Common fibular nerve, provides motor innervation to the anterior/ lateral leg and dorsal foot. It also provides sensory innervation to anterolateral leg and dorsal foot.
o Posterior femoral cutaneous nerve
o Pudendal nerve
Autonomic vs somatic nervous system
- The Somatic nervous system only uses acetylcholine as a neurotransmitter for both synapses to synapse and synapse to effector.
- The autonomic nervous system can use acetylcholine for synapse to synapse communication and: acetylcholine, epinephrine or norepinephrine for synapses to effector.
- Autonomic control of the heart is managed by both the sympathetic and parasympathetic divisions working together, this allows them to effect:
o Heart rate
o Force of contraction
o Vascular tone.
- The parasympathetic affects the heart by the vagus nerve and decreases heart rate force of constriction.
- The sympathetic affects the heart by the sympathetic nerves, and this increase heart rate and force of contraction.
- The autonomic branches from the cardiac plexus, containing left/ right vagus nerves and sympathetic trunk nerve. The visceral afferents return to the CNS (T1 – T4) , vagus carries sensory info on blood pressure and chemistry, while sympathetic truck relays cardiac pain and ischaemia.