Dominic Stone
The nervous system is a complex network that controls and regulates the body's functions and movements. It comprises the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord, while the PNS consists of all other nerves in the body, including those that connect to and control muscles. The somatic nervous system, a subdivision of the PNS, plays a crucial role in muscle control by transmitting signals from the brain to the muscles, enabling voluntary movements. On the other hand, the autonomic nervous system (ANS), a part of both the CNS and PNS, regulates involuntary muscle activities such as the beating of the heart. The ANS further divides into the sympathetic and parasympathetic nervous systems, which work together to maintain the body's functional balance.
| Characteristics | Values |
|---|---|
| Division | Somatic Nervous System and Autonomic Nervous System |
| Function | The somatic nervous system controls voluntary skeletal muscle movements and connects the CNS with organs and muscles to perform daily functions. The autonomic nervous system controls involuntary visceral functions, including heart rate, blood pressure, and glandular secretions. |
| Structure | The somatic nervous system is a single-neuron system with motor neurons in the brainstem or spinal cord and sensory neurons in the dorsal root ganglia. The autonomic nervous system is a two-neuron system with one neuron lying outside the CNS in the autonomic ganglia. |
| Peripheral Nervous System | The somatic nervous system is a component of the peripheral nervous system, which includes 12 pairs of cranial nerves and 31 pairs of spinal nerves. |
| Neuromuscular System | The neuromuscular system includes all the muscles in the body and their associated nerves, allowing for communication between the brain and muscles to facilitate movement and functions like breathing. |
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What You'll Learn
Somatic nervous system
The somatic nervous system is a subdivision of the peripheral nervous system, which is all of the nervous system except the brain and spinal cord. It allows us to move and control muscles throughout our body. The somatic nervous system is responsible for all the functions we can consciously influence, including moving our arms, legs, and other body parts. It is also responsible for the reflex arc, which involves using interneurons to perform reflexive actions.
The somatic nervous system is made up of 43 different segments of nerves, including 12 pairs of cranial nerves and 31 pairs of spinal nerves. These nerves help us perform daily functions. The cranial nerves are responsible for carrying information in and out of the brain. Spinal nerves carry somatosensory information and motor instructions out of the spinal cord. They branch out to form nerve fibres, which usually end at nerve endings in places like the tips of our fingers and toes.
The somatic nervous system contains afferent nerves travelling from the periphery towards the central nervous system (CNS) and efferent nerves responsible for sending signals from the CNS to the periphery. The main function of the somatic nervous system is to connect the CNS with organs and striated muscles to perform our daily functions. The basic motor pathway involves the upper motor neurons in the precentral gyrus (primary motor cortex), which sends signals through the corticospinal tract via axons in the spinal cord. The upper motor neuron releases neurotransmitters acetylcholine, which binds to nicotinic acetylcholine receptors of the alpha-motor neurons, creating a stimulus that propagates towards the neuromuscular junction (NMJ), which innervates muscles.
The somatic nervous system is structurally and functionally different from the autonomic nervous system. The somatic peripheral nervous system is a single-neuron system with the motor neurons in the brainstem or spinal cord and the sensory neurons in the dorsal root ganglia. The autonomic nervous system, on the other hand, is a two-neuron system with a neuron lying outside the CNS in the autonomic ganglia.
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Autonomic nervous system
The autonomic nervous system (ANS) is a network of nerves throughout the body that controls involuntary functions and unconscious processes. These include essential processes such as breathing, the heartbeat, blood pressure, digestion, and more. The ANS is always active, even when a person is asleep, and is key to survival.
The ANS is distributed throughout the central nervous system (CNS) and peripheral nervous system (PNS). It is composed of two main divisions: the sympathetic nervous system and the parasympathetic nervous system. These two systems work together to ensure the body responds appropriately to different situations. The sympathetic nervous system is responsible for the body's "'fight-or-flight' response, while the parasympathetic nervous system is responsible for "rest-and-digest" processes.
The sympathetic nervous system enhances organ activity, increasing the heart rate and blood pressure, constricting blood vessels in the skin, and dilating them in muscles. It also causes the body to release stored energy, increasing muscular strength. This division also causes palms to sweat, pupils to dilate, and hair to stand on end. The parasympathetic nervous system produces the opposite effect, decreasing heart rate and blood pressure, and increasing gastrointestinal motility and secretion.
The ANS controls the activities of the internal organs, including the heart, glands, smooth muscles, blood vessels, liver, kidneys, bladder, genitals, lungs, pupils, and digestive glands. It manages the width of the airways and the network of passages that carry air into and out of the lungs. It also manages the process of digestion from the small intestine to the colon.
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Motor neurons
Upper motor neurons originate in the cerebral cortex and travel to the brain stem or spinal cord. They are involved in controlling conscious movement.
There are three broad types of lower motor neurons: somatic motor neurons, special visceral efferent (branchial) motor neurons, and general visceral motor neurons. Somatic motor neurons are further divided into alpha, beta, and gamma motor neurons. Alpha motor neurons innervate extrafusal muscle fibres and are the primary means of skeletal muscle contraction. Beta motor neurons innervate both extrafusal and intrafusal fibres, and gamma motor neurons innervate intrafusal muscle fibres found within the muscle spindle. They regulate the sensitivity of the spindle to muscle stretching.
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Muscle stiffness and coordination
Muscle stiffness is a common issue, with most people experiencing acute muscle stiffness at some point in their lives. It is characterised by the sensation of tight, cramped, or painful muscles. GTOs (Golgi tendon organs) play a role in regulating muscle stiffness and coordination during movement, working with muscle spindles to ensure smooth transitions between contraction and relaxation, thereby improving overall motor control.
Muscle stiffness can be caused by a variety of factors, including dehydration, electrolyte imbalances, delayed-onset muscle soreness (DOMS), insect bites or stings, medications, anesthesia, muscle strains or sprains, periods of inactivity, and infections. In rare cases, muscle stiffness may be a symptom of a chronic condition, such as fibromyalgia, lupus, or stiff person syndrome (SPS). SPS is a rare autoimmune neurological disorder characterised by muscle stiffness, spasms, and rigidity, along with a lack of coordination, double vision, and slurred speech.
Simple treatments and home remedies can usually relieve muscle stiffness and improve coordination. These include alternating heat and cold therapy, massage, rest, warm baths, and stretching. In some cases, nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen may be recommended. If home remedies do not provide relief, physical therapy may be suggested to improve mobility, strength, and coordination, while addressing the root cause of stiffness.
The somatic nervous system, a component of the peripheral nervous system, is responsible for the voluntary control of body movements via skeletal muscles. It consists of afferent (sensory) and efferent (motor) nerves, connecting the central nervous system (CNS) with organs and skeletal muscles to perform daily functions. The somatic nervous system is involved in the reflex arc, utilising interneurons for reflexive actions.
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Neuromuscular junction
The neuromuscular junction (NMJ) is a synaptic connection between the terminal end of a motor nerve and a muscle (skeletal, smooth, or cardiac). It is the site for the transmission of action potential from nerve to muscle. The NMJ is also a site for many diseases and a site of action for pharmacological drugs.
The NMJ is composed of a presynaptic part (nerve terminal), a postsynaptic part (motor endplate), and an area between the nerve terminal and motor endplate (synaptic cleft). The presynaptic axons terminate in bulges called terminal boutons (or presynaptic terminals) that project toward the postjunctional folds of the sarcolemma. The sarcolemma at the junction has invaginations called postjunctional folds, which increase its surface area facing the synaptic cleft. These postjunctional folds form the motor endplate, which is studded with nicotinic acetylcholine receptors (nAChRs).
Acetylcholine is a neurotransmitter synthesized from dietary choline and acetyl-CoA (ACoA). It stimulates muscle tissue in vertebrates and some invertebrates. In vertebrates, the acetylcholine receptor subtype found at the NMJ of skeletal muscles is the nicotinic acetylcholine receptor (nAChR), a ligand-gated ion channel. Each subunit of this receptor has a characteristic "cys-loop" capable of binding acetylcholine and other ligands.
Diseases of the NMJ produce muscle weakness through mechanisms that may affect pre-synaptic, synaptic, or post-synaptic portions of the NMJ. Three main diseases that involve the NMJ are Myasthenia Gravis (MG), Lambert-Eaton syndrome (LES), and Botulism. Myasthenia Gravis is an autoimmune condition resulting in the production of auto-antibodies against acetylcholine receptors at the NMJ, decreasing their availability for acetylcholine and preventing muscle contraction.
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Frequently asked questions
The somatic nervous system is a subdivision of the peripheral nervous system, which is all of the nervous system except the brain and spinal cord. It allows you to move and control muscles throughout your body. It also feeds information from the senses of smell, sound, taste and touch into the brain.
The autonomic nervous system (ANS) is a part of the peripheral nervous system concerned with the innervation of involuntary structures such as the heart, smooth muscle and glands within the body. It is distributed throughout the CNS and PNS. It consists of two main divisions, the sympathetic and parasympathetic nervous systems.
The neuromuscular system includes all the muscles in the body and the nerves connecting them. Nerves called motor neurons send messages from the brain to muscles, making them contract and move.
