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Nerves are cells called neurons that carry messages to and from the brain through the spinal cord to muscles in the body. Motor nerves carry signals to the muscles or glands to help us move and function. Each motor neuron ending sits very close to a muscle fibre, and where they meet is called a neuromuscular junction. The motor neurons release a chemical, which is picked up by the muscle fibre, causing it to contract and make muscles move. Nerves are foundational to the nervous system, and they help us feel sensations, move our muscles, and control body functions like maintaining heart rate and digesting food.
| Characteristics | Values |
|---|---|
| Nerve cells | Also called neurons |
| Nerve function | Carry messages to and from the brain through the spinal cord to muscles in the body |
| Nerve location | Throughout the body, especially in the brain and spinal cord |
| Motor neurons | Carry signals to muscles or glands to help you move and function |
| Motor neuron endings | Sit very close to a muscle fibre |
| Neuromuscular junction | Where motor neuron endings sit with muscle fibres |
| Cranial nerves | Set of 12 nerves that send electrical signals between the brain and different parts of the head, face, neck and torso |
| Ulnar nerve | Powers almost all the small muscles in the hand |
| Median nerve | Supplies almost all the flexor muscles and all the pronator muscles of the forearm with nerves |
| Radial nerve | Wraps around the humerus bone, travels into the outside of the forearm and powers all the muscles that straighten the wrist and fingers |
| Brachial plexus | Group of nerves that branches from the cervical spine (neck) |
| Spinal nerves | Exit the vertebral column via an intervertebral foramen |
| Intercostal nerves | Segmental |
| Peripheral nerves | Range in diameter from 0.3 to 22 μm |
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What You'll Learn
Motor neurons and muscle fibres connect at the neuromuscular junction
Motor neurons are nerve cells that control the voluntary muscles of the trunk and limbs, and they affect speech, swallowing, and breathing. Each motor neuron ending sits very close to a muscle fibre, and the point at which they come together is called the neuromuscular junction.
At the neuromuscular junction, motor neurons release acetylcholine (ACh), a small-molecule neurotransmitter. This molecule diffuses across the synaptic cleft, a space between the neural and muscular components of the neuromuscular junction.
The ACh binds to nicotinic acetylcholine receptors (nAChRs) on the cell membrane of the muscle fibre, also known as the sarcolemma. These receptors are transmembrane proteins that function as ion channels. The binding of ACh to these receptors triggers a cascade of events, ultimately resulting in muscle contraction.
Disruptions or diseases affecting the neuromuscular junction can lead to muscle weakness and various symptoms. For example, Myasthenia Gravis is an autoimmune condition where antibodies are produced against the nAChRs at the neuromuscular junction, impairing muscle function.
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Cranial nerves are a set of 12 nerves that stem from the brain
Nerves are present throughout the human body and are a foundational part of the nervous system. They are like cables that carry electrical impulses between the brain and the rest of the body, helping us feel sensations and move our muscles.
The 12 cranial nerves are often referred to as pairs, as they serve the two sides of the brain and body. For example, the olfactory nerve has one nerve on the left side of the brain and one on the right. Each nerve has a specific function, with some having sensory functions, some having motor functions, and some having both.
The olfactory nerve (CN I) provides the sense of smell. The optic nerve (CN II) provides vision. The oculomotor nerve (CN III) opens and moves the eyes, and adjusts pupil width. The trochlear nerve (CN IV) moves the eyes towards or away from the nose. The trigeminal nerve (CN V) provides sensations in the eyes, face and mouth, and enables chewing. The abducens nerve (CN VI) moves the eyes from left to right. The facial nerve (CN VII) controls facial muscles and provides the sense of taste on the tongue. The vestibulocochlear nerve (CN VIII) provides the senses of hearing and balance. The glossopharyngeal nerve (CN IX) provides taste sensations and controls muscles for swallowing. It also plays a role in blood pressure regulation and saliva production. The vagus nerve (CN X) regulates automatic bodily processes, including digestion, blood pressure, heart rate, breathing, mood and saliva production.
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Spinal nerves carry sensations from joints and muscles to the spinal cord
Nerves are present throughout the human body and are one of the foundational parts of the nervous system. They send electrical signals that help us feel sensations and move our muscles. The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system. The CNS comprises the brain and spinal cord, which work together to transmit signals to and from the body.
The peripheral nervous system is a network of nerves that transmit signals from the body to the spinal cord, which then relays the signals to the brain. These signals help us feel sensations, such as touch, pain, temperature, and balance, and control voluntary movements. Spinal nerves are a part of the peripheral nervous system and carry sensations from joints and muscles to the spinal cord. There are 31 pairs of spinal nerves branching out from the spinal cord, and they can provide sensory function, motor function, or both.
For example, spinal nerves carry sensations from the skin, muscles, and joints to the spinal cord. These nerves also control some of our reflexes or involuntary responses, such as pulling your hand away from a hot stove. The Dorsal Ramus contains nerves that serve the dorsal portions of the trunk, carrying information to and from the skin and muscles of the back. The Ventral Ramus contains nerves that serve the remaining ventral parts of the trunk and the upper and lower limbs, carrying information to and from the body surface, structures in the body wall, and the limbs.
Additionally, spinal nerves can be affected by various conditions, such as cancer or compression, which can cause pain, sensory changes, or weakness. The spinal cord is also a major site of traumatic injury and the locus for many disease processes. Knowledge of spinal cord functional anatomy is essential for diagnosing cord damage and diseases.
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Nerve damage can cause muscle weakness and spasms
Nerves are present throughout the human body and are responsible for sending electrical signals that help us feel sensations and move our muscles. Motor nerves, for example, carry signals to our muscles or glands to help us move and function.
Neuromuscular diseases can also lead to muscle weakness and spasms. In some cases, the nerves are damaged and cannot carry messages from the brain as they should. As a result, muscles weaken and waste away (atrophy). This breakdown in communication between the nervous system and muscles can also lead to muscle fatigue and twitching.
Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of certain chemotherapy agents that damage peripheral nerves, including sensory nerves, motor nerves, and the autonomic nervous system. Carpal tunnel syndrome is another example of a disorder caused by pressure on the median nerve as it runs through the wrist.
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Radial nerves wrap around the humerus bone
Nerves are present throughout the human body and are a foundational part of the nervous system. They carry electrical signals that enable humans to feel sensations and move muscles. Motor nerves, for instance, carry signals to muscles or glands to help the body move and function.
The radial nerve is a major peripheral nerve of the upper limb. It supplies specific parts of the arm, forearm, wrist, and hand. The nerve has both motor and sensory functions. The motor branches stimulate the posterior arm muscles, posterior forearm muscles, and extrinsic wrist and hand extensors. The radial nerve wraps around the humerus bone laterally, supplying a branch to the medial head of the triceps brachii. The nerve gives function to the triceps muscles on the back of the arm to straighten the elbow.
The radial nerve is tightly bound within the spiral groove of the humerus, making it susceptible to damage in the event of a fracture of the humeral shaft. Radial nerve damage can cause wrist drop, a condition characterised by the inability to extend the wrist. The nerve then travels on the outside of the elbow (the lateral side) and into the outside of the forearm. In the forearm, the nerve powers all the muscles that straighten the wrist and fingers. It also provides sensation to the thumb side of the back of the hand.
The radial nerve then terminates by dividing into two branches: Deep branch (motor) – innervates the muscles in the posterior compartment of the forearm. Superficial branch (sensory) – contributes to the cutaneous innervation of the dorsal hand and fingers.
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Frequently asked questions
Muscle nerves terminate at the muscle fibres. Each nerve ending sits very close to a muscle fibre, and where they meet is called a neuromuscular junction.
Muscle nerves are nerves that carry signals to your muscles or glands to help you move and function. They are also known as motor nerves.
Some examples of muscle nerves include the ulnar nerve, the median nerve, the radial nerve, the facial nerve, and the vagus nerve.
