INTRO TO THE NERVOUS SYSTEM & BRAIN

The nervous system is the body’s control and communication center. The Nervous System has three main functions: Sensory Input Responds to Stimuli Integration Decides what to do with sensory input Motor Output

Organization of the Nervous System: The nervous system has two main divisions: Central Nervous System (CNS) Peripheral Nervous System (PNS)

Central Nervous System (CNS): the complex of nerve tissues that controls the activities of the body. Is made up of the brain and the spinal cord and is located in the midline of the body.

The Central Nervous System: The Central Nervous System is made up of the Brain and the Spinal Cord. Both the brain and spinal cord are protected by bone. The brain is enclosed by the skull. The spinal cord is surrounded by vertebrae. They are also both protected by 3 membranes known as the meninges. The space between the meninges are filled with cerebral spinal fluid (CSF) which protects/cushions the CNS.

Functions of the Spinal Cord: The spinal cord provides a means of communication between the brain and the peripheral nerves. If the spinal cord is severed we lose sensation and voluntary control of regions located below where the cord has been severed.

4 Major Regions of the Brain & Their Functions Cerebrum: Largest portion of the brain which carries out the higher thought processes including conscious thought, memory and problem solving. Has two halves that are connected by a bridge known as the corpus callosum. The two halves are: Left cerebral hemisphere Right cerebral hemisphere

4 Major Regions of the Brain & Their Functions Each hemisphere is divided into lobes Frontal Lobe– reasoning and movement Parietal Lobe– somatic sensing (touch) and taste Temporal Lobe– hearing Occipital Lobe– vision Cerebral Cortex– thin, highly convoluted outer layer that covers cerebral hemispheres. Accounts for sensation, voluntary movement, and conscious thought process. 2 1 4 3

4 Major Regions of the Brain & Their Functions The Diencephalon: The “Interbrain” posterior part of the forebrain that connects the midbrain with the cerebral hemispheres Contains the thalamus and the hypothalamus: Hypothalamus: An integrating center that helps maintain homeostasis by regulating hunger, sleep, thirst, body temperature, and water balance. Manufactures hormones and controls their release from the pituitary gland. Responsible for emotions. Thalamus: Receives all sensory input (taste, touch, smell, auditory, visual) Integrates info and sends to appropriate portion of cerebrum. Participates in higher mental function.

4 Major Regions of the Brain & Their Functions 3) Cerebellum: the part of the brain at the back of the skull which controls muscular activity Maintains posture and balance Ensures that all muscles work together smoothly and in a coordinated fashion. Assists in the learning of new motor skills

4 Major Regions of the Brain & Their Functions 4) Brainstem: the central trunk of the brain, which continues downward to form the spinal cord. Midbrain: Relay station between cerebrum and spinal cord or cerebellum Reflex sensors for visual, auditory and tactile responses Pons: Bridge between cerebellum and the rest of the CNS Together with medulla oblongata, regulates breathing 3. Medulla Oblongata: Contains reflex centers for regulating involuntary functions such as heartbeat, breathing, blood pressure, vomiting, coughing, sneezing, hiccupping and swallowing

THE PERIPHERAL NERVOUS SYSTEM Consists of nerves that carry sensory messages to the CNS and the motor commands from the CNS to the muscles and glands. Made up of 2 parts: 1. Nerves: Bundles of axons (fibres that conduct stimuli away from the cell) Fibers in the nerves can either be Sensory (Afferent) (carry info to CNS) or Motor (Efferent) (carry info away from CNS) Humans have spinal nerves attached to the spinal cord which takes impulses to and from the brain and peripheral nerves emerging from the openings in the vertebral column which takes impulses to and from the spinal cord. 2. Ganglia: enlargements associated with nerves that contain collections of nerve fibres.

PNS is divided into two parts: SOMATIC SYSTEM The somatic system is responsible for transmitting sensory information as well as for voluntary movement. This system contains two major types of neurons: Sensory neurons (afferent neurons) that carry information from the nerves to the central nervous system. Motor neurons (efferent neurons) that carry information from the brain and spinal cord to muscle fibers throughout the body. AUTONOMIC SYSTEM Responsible for regulating involuntary body functions, such as blood flow, heartbeat, digestion, and breathing. This system is further divided into two branches: The Sympathetic System The Parasympathetic System  

The sympathetic system regulates the “Fight or Flight” responses The sympathetic system regulates the “Fight or Flight” responses. It prepares the body to expend energy and deal with potential threats in the environment. The parasympathetic system helps maintain normal body functions and conserve physical resources.

The Nervous System & Impulse

What is a Neuron? A neuron is a cell that transmits nerve impulses between parts of the nervous system.

What is a Neuron? A neuron is made up of 3 parts: Cell Body - which contains the nucleus and other organelles. Dendrites - which are extensions leading toward the cell body that receive signals from other neurons and send them onto the cell body. Axon - which conducts nerve impulses away from the cell body toward other neurons or effectors.

Myelin Sheath The myelin sheath is the covering over the axons used for protection made up of specialized cells called SCHWANN CELLS The myelin sheath covers the axon but is interrupted in some areas forming gaps known as Nodes of Ranvier Made of Schwann Cells

Sensory neuron – take messages to the TYPES OF NEURONS Sensory neuron – take messages to the CNS and end in sensory receptors that detect changes in the environment 2. Interneuron – lies entirely within the CNS and receives inputs from sensory neurons and other interneurons. Sum up all the messages received before communicating with motor neurons. 3. Motor Neuron – takes messages away from the CNS to an effector and carry out our responses to environmental changes.

CONTROL OF THE NERVOUS SYSTEM The nervous system uses Nerve Impulses to convey information. Nerve impulses are electrical signals, which can be measured in millivolts (mV). Measures the electric potential difference (voltage) between the inside and the outside of the axon. https://www.youtube.com/watch?v=ZAmUjvgoO0A

1. Resting Potential Difference The axon is a membranous tube filled with axoplasm. When an axon is not conducting an impulse, the inside of the axon is negatively charged compared to the outside of the axon. Called resting potential because the axon is not conducting an impulse.

2. Action Potential Difference The rapid change in charge across an axomembrane and a nerve impulse occurs. This travels along the length of the axon. When a stimulus occurs, the axomembrane will detect and the charges will travel along the membrane. The stronger the stimulus, the more time the axon will ‘fire’ or charges will travel.

3. Synapse Transmission Every axon branches into fine endings, which are tipped by a small swelling called an axon terminal. These terminals lie very close to either the dendrite or the cell body of another neuron. This close proximity is called a synapse. 2 neurons at a synapse don’t physically touch each other.

3. Synapse Transmission The gap that separates each neuron is called the synaptic cleft. Communication between the 2 neurons at a synapse is carried out by molecules called neurotransmitters. Once signalled by an impulse, the neurotransmitters will travel across the synaptic cleft to the next neuron and bind with it’s membrane. The bind is formed because of receptor proteins on the membrane that bind with the neurotransmitter.

4. Response The response of the neurotransmitter binding with the protein outer layer of the neuron is 1 of 2: Excitation Causing an action to happen Inhibition Stopping an action from happening

Types of Neurotransmitters Acetylcholine (ACh): Found in both the CNS and the PNS. Norepinephrine (NE): Produced by the adrenal medulla and initiate the body’s response to an emergency situation – Fight or Flight

ADD THIS TO NOTES  Nerve Impulse from Stimulus to Response INTER Neurons