Pengantar sistem saraf (dr. djauhari)

Introduction to Nervous system

M. Djauhari WidjajakusumahDepartement of Physiology

Faculty of Medicine University of Indonesia

ORGANIZATION OF THE NERVOUS SYSTEM

• The nervous system is divided into two parts

o The central nervous system (CNS) o The peripheral nervous system (PNS)

afferent (or sensory) neurons efferent (or motor) neurons

• Information flow through the nervous system follows the basic reflex pattern

Silverthorn Human Physiol 5e, 2010

ORGANIZATION OF THE NERVOUS SYSTEM

o The central nervous system (CNS)

the brain and the spinal cord

the integrating center for neural reflexes

integrates information that arrives from the afferent branch of the PNS and determine whether a response is needed

sends output signals directing an appropriate response (if any) that travel through efferent neurons to their targets, which are mostly muscles and glands


ORGANIZATION OF THE NERVOUS SYSTEMo The peripheral nervous system (PNS)

Afferent (or sensory) neurons • Sensory receptors continuously monitor conditions in the internal and

external environments• Sensory receptors send information along afferent neurons to the central

nervous system

Efferent neurons• Somatic motor division,

– controls skeletal muscles• Autonomic division,

– controls smooth and cardiac muscles, exocrine glands, some endocrine glands, and some types of adipose tissue

– also called the visceral nervous system it controls contraction and secretion in the various internal organs [viscera, internal organs].

– divided into sympathetic and parasympathetic branchesSilverthorn Human Physiol 5e, 2010

FIGURE 8-1 Organization of the nervous system. The peripheral nervoussystem (PNS) sends information to the central nervous system (CNS) through afferent(sensory) neurons and takes information from the CNS to target cells via efferent neurons. The enteric nervous system can act autonomously or can be controlled bythe CNS through the autonomic division of the PNS.


● FIGURE 5-1 Organization of the nervous system.

FUNCTIONAL CLASSIFICATION

• Based on the direction in which a neuron transmits a nerve impulse.• Neurons found in the peripheral nervous system are of two basic

functions:

(1) Afferent neurons carry impulses towards the central nervous system (brain or spinal cord)

(2) Efferent neurons carry impulses away from the central nervous system

All afferent neurons carry sensory information, so they are also called sensory neurons

All efferent neurons affect the activity of muscles or glands, they are also called motor neurons

sensory = afferent motor = efferent

PERIPHERAL NERVOUS SYSTEM ORGANIZATIONPERIPHERAL NERVOUS SYSTEM ORGANIZATION

Types of Fibres in Peripheral and Cranial Nerves

Afferent • Somatic

General: sensory from cutaneous and muscle receptors Special: vision, hearing

• Visceral General: sensation from viscera Special: smell, taste

Efferent• Somatic

General: motor to skeletal muscle Special: efferent to eye, ear

• Visceral General: autonomic motor Special: motor to brachiomeric musculature

Vander et al.: Human Physiology: The Mechanism of Body Vander et al.: Human Physiology: The Mechanism of Body Function, 8th Ed, 2001Function, 8th Ed, 2001


Motor neuron with a myelinated axon. A motor neuron is comprised of a cell body (soma) with a nucleus, several processes called dendrites, and a long fibrous axon that originates from the axon hillock. The first portion of the axon is called the initial segment. A myelin sheath forms from Schwann cells and surrounds the axon except at its ending and at the nodes of Ranvier. Terminal buttons (boutons) are located at the terminal endings.

GENERAL PROPERTIES OF SENSORY SYSTEMS

• Begin with a stimulus, in the form of physical energy that acts on a sensory receptor.

• The receptor is a transducer that converts the stimulus into an intracellular signal, usually a change in membrane potential.

• If the stimulus is above threshold, action potentials pass along a sensory neuron to the central nervous system, where incoming signals are integrated. – Some stimuli pass upward to the cerebral cortex, reach conscious

perception – Others are acted on subconsciously, without our awareness.

• At each synapse along the pathway, the nervous system can modulate and shape the sensory information.



Vander et al.: Human Physiology: The Mechanism of Body Function, 8th Ed, 2001Vander et al.: Human Physiology: The Mechanism of Body Function, 8th Ed, 2001

FIGURE 10-1 Sensory receptors. (a) Simple receptors may have myelinated or unmyelinated axons. (b) This illustration shows a Pacinian corpuscle, which senses touch. (c) The cell illustrated is a hair cell, found in the ear.


Sensory Transduction Converts Stimuli into Graded Potentials• Receptors convert diverse physical stimuli, into electrical signals.

– transduction: the conversion of stimulus energy into information that can be processed by the nervous system.

• In many receptors, the opening or closing of ion channels converts mechanical, chemical, thermal, or light energy directly into a change in membrane potential.

• Some sensory transduction mechanisms include signal transduction and second messenger systems that initiate the change in membrane potential.

• The change in sensory receptor membrane potential is a graded potential called a receptor potential. – In some cells, the receptor potential initiates an action potential that

travels along the sensory ber to the CNS. – In other cells, receptor potentials influence neurotransmitter secretion by

the receptor cell, which in turn alters electrical activity in an associated sensory neuron. Silverthorn Human Physiol 5e,

2010

An afferent neuron with a receptor ending. The receptor potential arises at the nerve ending 1, and the action potential arises at the first node of the myelin sheath 2. (Vander et al.: Human Physiology: Vander et al.: Human Physiology: The Mechanism of Body Function, 8The Mechanism of Body Function, 8thth Ed, 2001, Fig 9-2) Ed, 2001, Fig 9-2)

Vander et al.: Human Physiology: The Mechanism of Body Function, 8th Ed, 2001Vander et al.: Human Physiology: The Mechanism of Body Function, 8th Ed, 2001

FIGURE 10-7 Sensory neurons use action potential frequency and duration to code stimulus intensity and duration; Silverthorn Human Physiol 5e, 2010

Synaptic transmission

Somatic Spinal Reflexes

General organization of the somatosensory General organization of the somatosensory system. system. The three basic levels of neural integration are the The three basic levels of neural integration are the receptor level, the circuit level, and the perceptual receptor level, the circuit level, and the perceptual level. The circuit level involves noncortical CNS level. The circuit level involves noncortical CNS centers, while the perceptual level involves cortical centers, while the perceptual level involves cortical sensory centers.sensory centers.

The first-order neurons are at the bottom of the The first-order neurons are at the bottom of the figure and include the sensory receptors. The figure and include the sensory receptors. The third-order neurons are the uppermost neurons in third-order neurons are the uppermost neurons in the figure, with cell bodies in the thalamus and the figure, with cell bodies in the thalamus and terminals in the somatosensory cortex. Second-terminals in the somatosensory cortex. Second-order neurons connect the first- and third-order order neurons connect the first- and third-order neurons.neurons.

FIGURE 13.2FIGURE 13.2

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Pengantar sistem saraf (dr. djauhari)

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