The Nervous System By Eko Widodo

The nervous system is one of the 2 control systems in our body. The nervous system is designed for fast action. It coordinates fast or rapid activities, such as muscle movement. Signaling is by electrical impulses, these are rapid, specific and produce an almost immediate response.

Functions of the Nervous System Sensory input – gathering information –To monitor changes occurring inside and outside the body –Changes = stimuli Integration –To process and interpret sensory input and decide if action is needed Motor output –A response to integrated stimuli –The response activates muscles or glands

Central nervous system (CNS) –Brain –Spinal cord Peripheral nervous system (PNS) –Nerve outside the brain and spinal cord –Spinal nerves carry impulses to and from the spinal cord –Cranial nerves carry impulses to and from the brain –PNS links all parts of the body by carrying impulses from the sensory receptors to the CNS and from the CNS to the appropriate muscle or gland Structural Classification of the Nervous System

Figure 7.1 Sensory (afferent) division –Nerve fibers that carry information to the central nervous system

Figure 7.1 Motor (efferent) division –Nerve fibers that carry impulses away from the central nervous system to muscles or glands

Figure 7.1 Motor (efferent) division –Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary

Organization of the Nervous System Figure 7.2

Neuroglia - Support, insulate and protect

Figure 7.3a Astrocytes –Abundant, star-shaped cells –Brace neurons –Form barrier between capillaries and neurons –Control the chemical environment of the brain

Microglia –Spider-like phagocytes –Dispose of debris Ependymal cells –Line cavities of the brain and spinal cord –Circulate cerebrospinal fluid Figure 7.3b–c

Nervous Tissue: Support Cells Oligodendrocytes –Produce myelin sheath around nerve fibers in the central nervous system Figure 7.3d

Figure 7.3e Nervous Tissue: Support Cells Satellite cells –Protect neuron cell bodies Schwann cells –Form myelin sheath in the peripheral nervous system

Neurons have 2 major functions – Irritability – ability to respond to a stimulus & convert it into a nerve impulse Conductivity – ability to transmit the impulse to other neurons, muscles or glands A nerve cell at rest is polarized, that is there is a charge across the membrane.

The ion concentration results in a net negative charge on inside of cell compared to ECF (extra cellular fluid) Ion Concentration

Starting a Nerve Impulse Depolarization – a stimulus depolarizes the neuron’s membrane Figure 7.9a–c A depolarorized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential in the neuron

Nerve Impulse Propagation The impulse continues to move Figure 7.9d–f

How Neurons Communicate at Synapses Figure 7.10

Drugs, sedatives and anesthetics can disrupt the permeability of the plasma membrane thereby blocking an AP. Cold and continuous pressure can hinder impulse transmission as they interprept the flow of blood (nutrients and oxygen) to neurons. Multiple sclerosis – destruction of myelin surrounding nerve, ends up short circuiting

The Reflex Arc Reflex – rapid, predictable, and involuntary responses to stimuli Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector Figure 7.11a

Simple Reflex Arc Figure 7.11b–c

Central Nervous System (CNS) CNS develops from the embryonic neural tube –The neural tube becomes the brain and spinal cord –The opening of the neural tube becomes the ventricles Four chambers within the brain Filled with cerebrospinal fluid

Regions of the Brain Cerebral hemispheres - cerebrum Diencephalon Brain stem Cerebellum Figure 7.12b

Cerebral Hemispheres (Cerebrum) Paired (left and right) superior parts of the brain Include more than half of the brain mass Figure 7.13a

Figure 7.14 Sensory and Motor Areas of the Cerebral Cortex