The Nervous System

The nervous system is a communication network that controls and coordinates most body actions. People are not generally conscious of some of these activities as they occur, such as regulating body temperature, breathing, or heart rate. Others, we consciously control, such as movement, talking, eating, and thinking.

The nervous system has two main parts: the central and the peripheral nervous system. The brain and spinal cord make up the central nervous system, or CNS. The nerves branching off the central nervous system make up the peripheral nervous system, or PNS. The PNS consists of nerves bundles made up of sensory and motor neurons.

Neurons

The nervous system is made up of cells called neurons. Neurons are long, thin cells that transmit electrical impulses. Neurons have many branched endings, called dendrites, which receive impulses from other neurons. An axon, or nerve fiber, carries nerve impulses to other neurons or to muscle. Neurons do not touch, but are separated by a tiny gap called a synapse. When an impulse arrives at the end of an axon, it releases chemicals that generate an impulse in the dendrites of the neighboring neuron.

 There are three types of neurons: sensory, motor, and association. Sensory neurons transmit nerve impulses from sense organs (eyes, ears, nose, tongue, and touch) to the brain. They also carry nerve impulses to the brain and spinal cord. Motor neurons transmit nerve impulses from the brain and spinal cord to a specific area of the body. A nerve impulse to a muscle, for example, may cause it to contract. Association neurons make up 90 percent of all neurons and are found only in the brain and spinal cord.

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Skull Anatomy

The Skull

 The skull is made up of 22 bones: the cranium includes eight bones that surround and protect the brain and 14 bones that form the face. In adults, all but one of the skull bones are fused together by immovable joints called sutures. The sutures lock the edges of the skull bones together, like pieces in a puzzle, to form a structure that is both rigid and strong. The mandible, or lower jaw, the only moveable skull bone, allows the mouth to open and close.

 In newborns, the skull bones are not completely fused; they are linked by fibrous membrane called fontanelles. Fontanelles allow the skull to be compressed slightly during birth and accommodate growth of the brain during early infancy. By one-and-a-half years of age, the skull sutures have formed and the fontanels have disappeared. 

Cranial Bones

The frontal bone forms the forehead. Two parietal bones form the sides of the cranial roof. Two temporal bones form the lower cranial sides. The occipital bone forms the cranial rear and floor. The ethmoid bone forms part of the nasal cavity. Shaped like a butterfly, the sphenoid bone forms the middle part of the cranial floor.

Facial Bones

The 14 facial bones provide the structure of the face and form the openings through which food, water, and air enter the body. Each of the following facial bones are paired: the maxillae form the upper jaw and front of the hard palate; the zygomatic bones form the cheeks; the nasal bones form the bridge of the nose; the lacrimal bones form part of the orbit, or eye socket; the palatine bones form the rear of the hard palate; and the inferior nasal conchae divide the nasal cavity. The vomer is a single bone that makes up part of the nasal septum, which divides the nostrils, and the mandible forms the lower jaw. The maxillae and mandible secure the teeth.

                           

 Small holes in the skull bones, called foraminae, and canals enable blood vessels, such as the carotid arteries and nerves, to enter and leave the skull. The spinal cord passes through a largest hole, called the foramen magnum, in the base of the cranium to join the brain. The occipital condyles on either side of the foramen magnum articulate with the first vertebra
(C1) of the spine to permit up-and-down movement of the head.

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brain parts

The brain has three main parts

the cerebrum, the cerebellum, and the brain stem. The brain is divided into regions that control specific functions.

 1-The cerebrum

 Frontal Lobe

• Behavior
• Abstract thought processes
• Problem solving
• Attention
• Creative thought
• Some emotion
• Intellect
• Reflection
• Judgment
• Initiative
• Inhibition
• Coordination of movements
• Generalized and mass movements
• Some eye movements
• Sense of smell
• Muscle movements
• Skilled movements
• Some motor skills
• Physical reaction
• Libido (sexual urges)  

Occipital Lobe

• Vision
• Reading 

 Parietal Lobe

• Sense of touch (tactile senstation)
• Appreciation of form through touch (stereognosis)
• Response to internal stimuli (proprioception)
• Sensory combination and comprehension
• Some language and reading functions
• Some visual functions

Temporal Lobe

• Auditory memories
• Some hearing
• Visual memories
• Some vision pathways
• Other memory
• Music
• Fear
• Some language
• Some speech
• Some behavior amd emotions
• Sense of identity

Right Hemisphere (the representational hemisphere)

• The right hemisphere controls the left side of the body
• Temporal and spatial relationships
• Analyzing nonverbal information
• Communicating emotion

Left Hemisphere (the categorical hemisphere)

• The left hemisphere controls the right side of the body
• Produce and understand language

Corpus Callosum

• Communication between the left and right side of the brain

2-The cerebellum

• Balance
• Posture
• Cardiac, respiratory, and vasomotor centers

3-The brain stem

• Motor and sensory pathway to body and face
•  Vital centers: cardiac, respiratory, vasomotor

Hypothalamus

• Moods and motivation
• Sexual maturation
• Temperature regulation
• Hormonal body processes

Optic Chiasm

• Vision and the optic nerve

Pituitary Gland

• Hormonal body processes
• Physical maturation
• Growth (height and form)
• Sexual maturation
• Sexual functioning

Spinal Cord

• Conduit and source of sensation and movement

Pineal Body

• Unknown

Ventricles and Cerebral Aqueduct

• Contains the cerebrospinal fluid that bathes the brain and spinal cord

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