Nervous System

NERVOUS SYSTEM

The nervous system is our body's decision and communication center. The central nervous system (CNS) is made of the brain and the spinal cord and the peripheral nervous system (PNS) is made of nerves. Together they control every part of your daily life, from breathing and blinking to helping you memorize facts for a test. Nerves reach from your brain to your face, ears, eyes, nose, and spinal cord... and from the spinal cord to the rest of your body. Sensory nerves gather information from the environment, send that info to the spinal cord, which then speed the message to the brain. The brain then makes sense of that message and fires off a response. Motor neurons deliver the instructions from the brain to the rest of your body. The spinal cord, made of a bundle of nerves running up and down the spine, is similar to a superhighway, speeding messages to and from the brain at every second.

CEREBRAL HEMISPHERES.

By means of a prominent groove, called the longitudinal fissure, the brain is divided into two halves called hemispheres. 

The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the medial longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres.

CEREBRAL HEMISPHERES.

By means of a prominent groove, called the longitudinal fissure, the brain is divided into two halves called hemispheres. 

The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the medial longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres.

The brain is made of three main parts:

1.Forebrain  (cerebrum)

The forebrain is divided into two main sections:

a)Telencephalon

i) Cerebrum (Cerebral Cortex)

• The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe

·         Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving

·         Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli, Spatial processing

·         Occipital Lobe- associated with visual processing

·         Temporal Lobe- associated with perception and recognition of auditory stimuli, memory,  speech, and understanding language

ii)Basal Ganglia

• Movement regulation
• Skill learning

iii)Limbic System (hippocampus and amygdala)

•  Memory formation
• Responsible for the formation of long-term memories
• Damage to this area does not destroy old memories; rather, new memories can no longer be formed
• Emotion processing

b)Diencephalon

i)Thalamus

• Primary "gate" between sensory or motor neurons in the PNS and the cerebral hemispheres in the CNS
• The Thalamus is a collection of pathways that connects peripheral sensory organs to the various sensory corticies.

ii)Hypothalamus

• The Hypothalamus controls the visceral nervous system, guiding actions such as thirst, temperature regulation, and glanduar secretions in the organs.
• Maintains homeostasis: like a thermostat, it increases or decreases metabolism in order to regulate body activity

2.Midbrain (cerebellum)

Cerebellum

• Controls posture and walking
• Handles reflexes of eye movements

3.Hindbrain (medulla)

a)myelencephalon

• Medulla  (medulla oblongata)
• Full name: Medulla Oblongata ("oblong marrow")
• Connects the spinal cord to pons

b)metencephalon

• Pons
• Full name: Pons Varolii. Originally means 'bridge'
• Bridges the cerebrum and the cerebellum through cerebellar peduncles

The Structure of the Neuron  

 Neurons are specialized cells that transmit chemical and electrical signals in the brain; they are the basic building blocks of the central nervous system.  The primary components of the neuron are the soma (cell body), the axon (a long slender projection that conducts electrical impulses away from the cell body), dendrites (tree-like structures that receive messages from other neurons), and synapses (specialized junctions between neurons). Some axons are covered with myelin, a fatty material that acts as an insulator and conductor to speed up the process of communication

Dendrites - a neuron's branches that receive information from other neurones and transmit it toward the cell body.

Cell Body - The part of the neuron that keeps it alive and determines whether or not it will fire.

Axon - a neuron's extending fibre that conducts impulses away from the cell body and transmits them to other neurones.

Myelin sheath - A fatty insulation that may surround the axon of the neurone

Synapse - place where transmission of nerve impulses go from one neurone to the next.   

- Includes the axon terminal, the synaptic cleft, and receptor sites in membrane of the next cell.

Neurotransmitter - a chemical substance(acetylcholine) that is released by a transmitting neuron at the synapses and that alters the activity of a receiving neuron.

 acetylcholine - transmits between nerves and muscles   

  dopamine - important in "reward" system and also seems to play inhibitory role, 

                       important in schizophrenia & Parkinson's syndrome

  serotonin - involved in sleep, dreaming, arousal & emotions