Nervous and Endocrine Systems: Functions and Parts

Nervous and Endocrine Systems

The nervous system receives external and internal stimuli, interprets them, and decides an appropriate response. The response is executed by the effector organ or tissue. Nervous tissue is made up of cells called neurons.

Stimulus → Nervous System → Effectors → Muscles, Glands

Neuron Structure

• Cell body: The central part of the neuron.
• Dendrites: Extensions of the cell body. They receive the nerve impulse and transmit it to the cell body.
• Axon: A long fiber extending from the cell body. It transmits the nerve impulse to other neurons or effector cells.
• Myelin sheath: This layer protects the axon and increases the speed of the nerve impulse.
• Axon terminals: These are located at the end of the axon. They contain neurotransmitters, which are chemical substances that enable the impulse to travel from one neuron to another neuron or to an effector cell.

Transmission of Nerve Impulses: Synapse

Neurons generate electrical and chemical changes that are transmitted from one neuron to another. This event is called a synapse. There is NO physical contact between neurons.

1. The nerve impulse is transmitted from the dendrites through the axon of the presynaptic neuron.
2. When the electric signal reaches the axon terminal, neurotransmitters are released into the synaptic cleft. (Neurotransmitters are stored in vesicles in the axon terminal.)
3. The neurotransmitters join receptors in the dendrites of the postsynaptic neuron, and the nerve impulse continues along it.

Parts of the Nervous System

PNS (receptors and sensory organs): receive stimuli → CNS (brain and spinal cord): process information → PNS (motor neurons): transmit orders → EFFECTORS (glands and skeletal, smooth, and cardiac muscles): carry out the action.

The Endocrine System

The endocrine system is made up of a coordinated group of glands called endocrine glands. They are called endocrine (endo means internal) because they release hormones directly into the bloodstream. The glands respond to stimuli by producing hormones that travel through the bloodstream. When a hormone reaches the target cell (the one that has specific receptors for it), it joins it and provokes a response.

Central Nervous System (CNS)

The Brain

• Cerebrum: Interprets information, regulates muscular activity, and intellectual processes. The surface is folded (convolutions) and has a superficial layer of grey matter, and the internal layer is of white matter.
• Thalamus and Hypothalamus: Involved in hormone production.
• Cerebellum: Controls posture and balance.
• Brain stem: Connects the brain to the spinal cord. Regulates blood pressure, heartbeat, and respiration.

The Spinal Cord

Nervous tissue that runs through the spine. It connects the brain with the PNS and controls reflex actions. The grey matter is located in the internal layer, and the white matter is superficial.

Peripheral Nervous System (PNS)

It is composed of nerves. Nerves are a group of axons of different neurons bundled together and covered by connective tissue.

Types of Nerves

Depending on their function:

• Sensory nerves (receptor to CNS)
• Motor nerves (CNS to effectors)
• Mixed nerves (both)

Depending on their location:

• Cranial nerves (connect the brain with the organs without passing through the spinal cord - 12 pairs)
• Spinal nerves (connect the spinal cord with the torso and limbs - 31 pairs)

Peripheral Nervous System Subsystems

Somatic Nervous System

This system connects the receptors to the CNS and the CNS to the skeletal muscles. It is responsible for voluntary actions and reflex actions.

Voluntary Actions

The receptor detects a stimulus, which travels to the spinal cord and cerebrum. There, a response is prepared, which the effector organ will carry out.

Reflex Actions

The stimulus detected by the receptor travels to the spinal cord, where a response is prepared without having passed through the cerebrum.

Autonomic Nervous System

It connects the receptors to the CNS and the CNS with the internal organs and glands. It sends INVOLUNTARY RESPONSES.

• The parasympathetic nervous system provokes relaxation, and the organs work more slowly and less intensely.
• The sympathetic nervous system controls most of the body's organs so that they work more effectively under stress.

The autonomic nervous system consists of the sympathetic nervous system and the parasympathetic nervous system. These have opposing functions and are coordinated.