Chapter 13
Nervous System
Table of Content
- Overview of the Nervous system
- The central nervous system
- The limbic system and higher mental functions
- The peripheral nervous system
- Drug abuse
- Picture references
- Overview of the Nervous system
- Has two major divisions: the central nervous system and the peripheral nervous system.
- The nervous system has three major functions:
- Reception of input
- Integration of data
- Generate motor output
- Nervous Tissue
- Two types of cells: neurons and neuroglia.
- Neurons-transmit nerve impulse between parts of the nervous system.
- Neuroglia- support and nourish neurons.
- Neuron structure
- The type of neurons
- Sensory neurons-are special structures that detect changes in the environment.
- Interneuron-lies entirely within the CNS.
- Motor neurons-takes nerve impulses away from the CNS to an effectors.
- Effectors carry out our responses to environmental changes, whether they are external or internal.
- Composed of dendrites, a cell body, and axon.
Myelin Sheath
- Myelin Sheath
- Long axons are covered by a myelin sheath.
- The Nerve impulse
Resting potential-more Na+ outside the axon and more K+ inside the axon. The axon does not conduct an impulse.
Action potential- a change in polarity across the axonal membrane as a nerve impulse occurs.
- The synapse
- When a neurotransmitter is released into a synaptic cleft, transmission of a nerve impulse occurs.
- Neurotransmitter transmits from on neuron to the next so neurons don’t physically touch.
Synapse
- The central nervous system
CNS
- The spinal cord and the brain make up the CNS.
- Where sensory information is received and motor control is initiated.
- Both the brain and spinal cord are protected in a membrane known as meinges.
- The Spinal Cord
- Extends from the base of the brain through a large opening in the skull called the foramen magnum and into the vertebral canal formed by openings in the vertebrae.
- Grey matter of the spinal cord contains neuron cell bodies.
- White matter consists of myelinated axons that occur in tracts.
- The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord.
- Conduction to and from brain; carries out reflex actions.
Spinal Cord
- The Brain
- The cerebrum is the largest portion of the brain in humans. Is the last center to receive sensory input and carry out integration before commanding voluntary motor responses.
- Four major parts of the brain are: cerebrum, diencephalon, cerebellum, and the brain stem.
- Has two cerebral hemispheres connected by the corpus callosum.
- Shallow grooves called sulci divide each hemisphere into lobes
- Frontal lobe-the most ventral of the lobes.
- Parietal lobe- is dorsal to the frontal lobe.
- Occipital lobe- is dorsal to the parietal lobe.
- Temporal lobe- lies inferior to the frontal and parietal lobe.
- Each lobe is associated with particular functions.
- The cerebral cortex- is a thin but highly convoluted outer layer of gray matter that covers the cerebral hemispheres.
- Covers the cerebrum.
- Diencephalon- contains the hypothalamus and thalamus, maintains homeostasis, and receives sensory input.
- Cerebellum- sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements.
- Brain stem- contains the midbrain, pons, and medulla oblongata, relay station and medulla had reflex centers.
the Lobes in the Brain
- The limbic system and higher mental functions
- Limbic system
- Functions of limbic system-
- Blend primitive emotions and higher mental functions into a united whole.
- The amygdala can cause experiences to have emotional overtones, and it creates the sensation of fear.
- The hippocampus plays a crucial role in learning and memory. It’s involved in storing and retrieving memories.
Limbic System
- Higher mental Functions
- Memory is the ability to hold a thought in mind or to recall events from the past, ranging from a word we learned only yesterday to an early emotional experience that has shaped our lives.
- Learning takes place when we retain and utilize past memories.
- Type of memory:
- Short term memory
- Long term memory
- Semantic memory
- Episodic memory
- Skill memory
- Long-term memory is stored in bits and pieces throughout the sensory association areas of the cerebral cortex.
- Language depends on semantic memory.
4. The peripheral nervous system
- The PNS contains only nerves and ganglia.
- Cranial nerves take impulses to and from the brain. There are 12 pairs of cranial nerves.
Cranial Nerves
Spinal nerves take impulses to and from the spinal cord. There are 31 pairs of spinal nerves.
- The PNS is divided into the somatic system and the autonomic system.
- Somatic System
- Serve the skin, skeletal muscle, and tendons.
- Reflexes are automatic responses to a stimulus in the somatic system. A reflex occurs quickly, without us thinking!!
- Autonomic System
- Regulates the activity of cardiac and smooth muscles and glands.
- A function involuntarily, has two systems that normally cause opposite responses.
- Sympathetic Division
- Parasympathetic division
- Drug abuse
- Drug abuse is apparent when a person takes a drug at a dose level and under circumstances that increase the potential for a harmful effect.
- Drug abuse affect the limbic system
- And promote or decrease the action of a particular neurotransmitter.
- Alcohol
- Is dangerous to the body and brain.
- CNS, alcohol acts as a depressant and influences many brain regions and neurotransmitter.
- Nicotine
- Acts as a stimulant.
- In the PNS, nicotine imitations acetylcholine and increases skeletal muscles activity, heart rate and blood pressure.
- Cocaine
- Powerful stimulant in the CNS.
- Methamphetamine
- Acts as a stimulant.
- Death can occur.
- Heroin
- Acts as a depressant.
- Is the most abuse opiate because it is rapidly delivered to the brain.
- Marijuana
- Acts as a psychoactive.
- Has influence in the brain.
- Has a reaction to the CNS.
- Has some medical use to people who suffer from illness.
Picture References:
http://www.issaonline.com/trial/unit1/images/nervoussystem.jpg
http://z.about.com/f/p/440/graphics/images/en/8679.jpg
http://academic.kellogg.cc.mi.us/herbrandsonc/bio201_McKinley/f14-3a_structures_in_a__c.jpg
http://medicalimages.allrefer.com/large/central-nervous-system-1.jpg
http://people.eku.edu/ritchisong/spinalcord5.gif
http://www.wright.edu/academics/honors/institute/images/brain_diagram.jpg
http://www.macalester.edu/psychology/whathap/ubnrp/dopahypoweb04/limbicsystem.jpg
http://mybrainic.com/images/otak_1_eng.gif
http://www.macalester.edu/psychology/whathap/UBNRP/vagus05/Vagus_pics/cranialnerves.jpg
Chapter 14
Senses
Table of Content
- Sensory Receptors and Sensations
- Proprioceptors and Cutaneous Receptors
- Senses of Taste and Smell
- Sense of Vision
- Sense of Hearing
- Sense of Equilibrium
- Picture References
- Sensory Receptors and Sensations
· Function of a sensory receptor is to detect certain type of stimuli.
· Type of Sensory Receptors
o Chemoreceptor-respond to chemical substances in the immediate vicinity. Ex. Receptors for taste and smell.
o Photoreceptor-respond to light energy. Ex. Vision. Eyes.
o Mechanoreceptor- are stimulated by mechanical forces, which most often result in pressure of some sort. Ex. From pressure, sound waves and gravity. Hearing.
o Thermoreceptor- sensory receptor that is sensitive to changes in temperature. Ex. Body temperature.
· How Sensation Occurs
o Sensation is the conscious perception of stimuli that occurs after sensory receptors generate a nerve impulse that arrives at the cerebral cortex.
- Proprioceptors and Cutaneous Receptors
· Proprioceptors
o Are mechanoreceptors involved in reflex actions that maintain muscle tone and thereby the body’s equilibrium and posture.
o To assist the brain in knowing the position of the limbs and space
· Cutaneous Receptors
o Are found in the skin
o Are for touch, pressure, temperature, and pain.
· Pain Receptors
Sensory receptors in human skin
- Senses of Taste and Smell
· Taste and smell are called chemical senses because their receptors are sensitive to molecules in the food we eat and the air we breathe.
· Taste and smell are due to chemoreceptors that are stimulated by molecules in the environment.
· Sense of Taste
o About 3,000 taste buds are located mostly on the tongue.
o Most taste buds lie along the walls of the papillae.
o At least four primary types of taste:
o Sweet
o Sour
o Salty
o Bitter
o Umami, the fifth taste, may exist for certain flavor.
Type of taste locations Sense of Taste and their cells
o Taste buds open at a taste pore.
o Microvilli of taste cells have receptor proteins fro molecules that cause the brain to distinguish, sweet, sour, salty, and bitter tastes.
· Sense of Smell
o Approximately 80%-90% of what we perceive as “taste” actually is due to sense of smell
o The cilia of olfactory cells have receptor proteins for molecules that cause the brain to distinguish odors.
o Olfactory cells are located high in the roof of the nasal cavity.
o The olfactory bulbs have direct connections with the limbic system and its center for emotions and memory.
A Human Eye
· Vision depends on the eye, the optic nerves, and the visual areas of the cerebral cortex.
· Anatomy and Physiology of the Eye
o The eye has three layers, or coats:
o The sclera (outer layer) protects and supports the eyeball.
o The choriod (middle pigmented layer) absorbs stray light rays.
o The retina (inner layer) contains the rod cells (sensory receptors for dim light) and cone cells (sensory receptors for bright light and color).
o The lens brings the light rays to focus on the retina. To see a close object, visual accommodation occurs as the lens rounds up.
o The pathway for vision begins once light has been focused on the photoreceptors in the retina.
o Functions of photoreceptors
o Rod cells
o Cone cells
§ Both have an outer segments joined to an inner segment by a stalk.
· Abnormalities of the Eye
o Color blindness
o Misshapen eyeballs
o Complete color blindness is extremely rare.
o Nearsighted people can see close objects better than they can see objects at a distance.
o Farsighted people can see distant objects better than they can see close objects.
o Astigmatism, is when the cornea or lens is uneven, the image is fuzzy. The light rays cannot be evenly focused on the retina.
The Human Ear
· The ear has two sensory functions:
o Hearing and balance.
o Both located in the inner ear.
o Each consists of hair cells with stereocilia that are sensitive to mechanical.
o There are mechanoreceptors.
o Hearing depends on the ear, the cochlear nerve, and the auditory areas of the cerebral cortex.
· Anatomy and Physiology of the Ear
o The ear has three parts:
o In the outer ear, the pinna and the auditory canal direct sound waves to the middle ear.
o In the middle ear, the tympanic membrane and the ossicles (malleus, incus, and stapes) amplify sounds waves.
o In the inner ear, the semicircular canals detect rotational equilibrium; the utricle and saccule detect gravitational equilibrium; and the cochlea house the spiral organ, which contains mechanoreceptors for hearing.
o The auditory pathway begins when the outer ear receives and the middle ear amplifies sound waves that then strike the oval window membrane.
o Mechanoreceptors allow us to hear and are located in the inner ear. They function by sensitive to mechanical stimulation.
- Sense of Equilibrium
· The ear also contains mechanoreceptors for equilibrium.
· Rotational Equilibrium Pathway
· Mechanoreceptors in the semicircular canals detect rotational and/or angular movement of the head. (Rotational equilibrium).
· Gravitational Equilibrium Pathway
· The receptors are located: Utricle and saccule
· It’s function is: Utricle and saccule contain hair cells with sterocilia embedded in an otolithic membrane; when the head bends, otoliths are displaced causing the sterocilia to bend.
Picture References:
http://fig.cox.miami.edu/~cmallery/150/neuro/c7.49.3.skin.jpg
http://library.thinkquest.org/3750/images/tastebud.gif
http://classes.midlandstech.com/bio112/taste%20buds.jpg
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