SBI 4U JANUARY 14 TH, 2013 The Importance of the Nervous System

Nervous System & Homeostasis Human brain – control centre of the body If brain is damaged, other parts of your body effected as well Nervous system, body’s interface with external environment and the control system that manages the internal environment Physical, cognitive or physiological changes

Neural Signalling Neuron: specialized nerve cell, functioning unit of nervous system Neural signalling: communication by neurons – process by which an animal responds appropriately to stimuli – reception, transmission, integration and response

Neural Signalling Reception: detection Transmission: movement of a message Integration: sorting and interpretation, determining appropriate response Response: output or action

Neural Signalling 3 functional classes of neurons: 1. Afferent neurons: transmit stimuli to; 2. Interneurons: integration info to formulate response; 3. Efferent neurons: carry response signals to effectors

Neural Signalling Efferent neurons that carry signals to skeletal muscles are called motor neurons Stimulus  afferent neurons  interneurons  efferent neurons  effectors  action

Neuron Structure Vary in shape & size Enlarged cell body and 2 extensions Cell body (nucleus and most organelles)  synthesizes most proteins, carbs and lipids Dendrites receive signals and transmit toward cell body Axons conduct signals away from cell body to another neuron or effector Axon hillock Neuronal circuits

Neuron Structure

Neuron Support System Glial cells: structural support and metabolism of nerve cells Schwann cells, form layers of membrane called myelin sheaths around axons, gaps between Schwann cells, called nodes of Ranvier, expose axon membrane to extracellular fluids  speeds up the rate of electrical impulses Division and brain tumors

Organization of Nervous System CNS and PNS CNS: coordinating centre  brain and spinal cord PNS: communicates with CNS. Subsystem PNS: afferent system (receives input through receptors) and the efferent system (carries signals to muscles and glands)

Organization of Nervous System Efferent System divided into somatic system (communicates with skeletal muscles) and autonomic system (communicates with smooth muscles and glands) Somatic system: voluntary (some exceptions) Autonomic system: involuntary, digestion, secretion by sweat glands, circulation of the blood, etc;

Organization of the Nervous System Autonomic System  sympathetic and parasympathetic divisions Sympathetic: dominates during stress, danger, excitement or physical activity Parasympathetic: dominates during quiet, low- stress situations, such as relaxation

Reflex Arc Neural circuit  5 components: receptor, the afferent neuron, the interneuron, the efferent neuron, and the effector Reflex arc: travels through spinal cord, but does not require coordination from brain Ex: when your finger touches a very hot object