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The Nervous System Chapter 7 © 2013 John Wiley & Sons, Inc. All rights reserved.
Every conscious action that occurs in your body is governed by the nervous system (NS) – Functions include: Communication from one end of the body to another Collection and integration of internal and external stimuli Formulation of appropriate responses Most unconscious (or automatic) actions also are governed by the NS The immediacy of the NS response sets it apart from other control systems of the body – It is responsible for maintaining homeostasis – The NS works in concert with the endocrine system © 2013 John Wiley & Sons, Inc. All rights reserved.
Central Nervous System (CNS) – Composed of the brain and spinal cord – Encased by the axial skeleton and covered by meninges – Main integration system of the body Peripheral Nervous System (PNS) – Composed of all neural tissue other than the brain and spinal cord – Includes: all the afferent and efferent neurons that extend from the CNS the autonomic, sensory, and somatic nerves of the body © 2013 John Wiley & Sons, Inc. All rights reserved.
Sensory information enters the CNS, which analyzes it and then sends a motor response through the PNS to muscular or glandular tissue Information reaches the CNS from the afferent division of the PNS – The PNS picks up this information with one of three types of receptors Special senses (sight, hearing, taste, smell) General sensory receptors (external temp., light, touch, pain) Visceral receptors (proprioception, organ functions) Motor responses are sent through the efferent division of the PNS © 2013 John Wiley & Sons, Inc. All rights reserved.
The somatic division is involved in conscious movement – It regulates voluntary movement of skeletal muscles The autonomic division governs the body’s responses to changes in homeostasis with involuntary, unconscious reactions – It regulates functions such as blood vessel diameter and stomach activity – The autonomic nervous system has two subdivisions Sympathetic NS Parasympathetic NS © 2013 John Wiley & Sons, Inc. All rights reserved.
Sympathetic NS – Includes nerves that control the body when it is actively moving and burning energy Fight or flight responses – Nerves in the thoracic and lumbar regions of the spinal cord Parasympathetic NS – Includes nerves responsible for digestion, energy storage and relaxation Rest and digest responses – Nerves in the cranial and sacral regions of the spinal cord Most body organs are innervated by both the Sympathetic NS and Parasympathetic NS – To maintain homeostasis © 2013 John Wiley & Sons, Inc. All rights reserved.
SYMPATHETIC NSPARASYMPATHETIC NS © 2013 John Wiley & Sons, Inc. All rights reserved.
The NS contains neurons and neuroglial cells The neuron is the functional unit of the NS – Functions include: Carrying sensory information to the brain Formulating responses Sending responses to organs – Neurons arrange into bundles called nerves Neuroglia are the supporting cells of nervous tissue © 2013 John Wiley & Sons, Inc. All rights reserved.
The three classes of neurons are based on function – Sensory neurons detect conditions in the environment or body – Motor neurons carry instruction to the body – Interneurons connect sensory and motor neurons © 2013 John Wiley & Sons, Inc. All rights reserved.
Reflexes are rapid responses to sensory stimuli – The stimulus from a sensory neuron bypasses the brain and instead runs through an interneuron within the spinal cord – The motor neuron then transmits an immediate response to the effector organ © 2013 John Wiley & Sons, Inc. All rights reserved.
The membrane potential results from the difference in ion concentrations between the two sides of a cell membrane Measured as electrical differences The membrane potential of a neuron during a typical nerve impulse alternates between –70 mV and +30 mV At rest, the inner side of a neuron’s membrane is negatively charged relative to it’s outer side and its membrane potential is -70 mV Variations in ion concentration across the cell membrane allow neurons to generate action potentials © 2013 John Wiley & Sons, Inc. All rights reserved.
Ions cannot simply diffuse through the lipid bilayer of the cell membrane, they must travel through channel proteins Voltage-gated channels - Respond to trans-membrane voltage changes Ligand-gated channels - Chemically regulated Mechanically-regulated channels - Respond to distortions of the membrane surface © 2013 John Wiley & Sons, Inc. All rights reserved.
An action potential is a brief change in electrical conditions at a neuron’s membrane – When a neuron “fires”, the charge differential across the neuron’s membrane suddenly reverses polarity – Action potentials are “all or nothing” events IPSPs and EPSPs also influence the generation of action potentials © 2013 John Wiley & Sons, Inc. All rights reserved.
Graded responses can be obtained by hyperpolarizing or depolarizing individual neural membranes Excitatory postsynaptic potentials (EPSPs) – Cause slight depolarization of the neuron Inhibitory postsynaptic potentials (IPSPs) – Hyperpolarize the neuron – The membrane potential is further from that needed to generate an action potential, so a larger stimulus is required to begin an action potential © 2013 John Wiley & Sons, Inc. All rights reserved.
Synapses separate one neuron from another Neurotransmitters are chemicals used to transmit the nerve impulse from one cell to the next – Diffuse across the synaptic cleft © 2013 John Wiley & Sons, Inc. All rights reserved.
The volume of the human brain is about 1250 cm 3 The human brain weighs about 1,400 grams The cerebrospinal fluid and meninges protect and nourish the CNS – The meninges are a series of three consecutive tissue coverings between the nervous tissue and the bone – The CSF functions to maintain uniform pressure within the brain and spinal cord © 2013 John Wiley & Sons, Inc. All rights reserved.
Dura mater – Tough connective tissue layer immediately beneath the skull Arachnoid mater – A thin, fragile layer which resembles a spider web – Cerebrospinal fluid flows between the strands of the arachnoid mater Pia mater – The innermost layer, extremely thin and attached to neurons Meningitis is an inflammation of these three layers © 2013 John Wiley & Sons, Inc. All rights reserved.
Provides a constant environment for the CNS Its is continuously produced and absorbed, creating a constant flow – Ventricles make CSF CSF helps maintain the blood-brain barrier – Permits passage of only certain ions and nutrients © 2013 John Wiley & Sons, Inc. All rights reserved.
The brain has 4 main parts – The brain stem – The cerebellum – The diencephalon – The cerebrum © 2013 John Wiley & Sons, Inc. All rights reserved.
The oldest part of brain Made up of the – mid brain, medulla oblongata, and pons Regulates – heart rate, breathing, and blood pressure Has reflex centers for – sneezing, coughing, hiccupping and swallowing © 2013 John Wiley & Sons, Inc. All rights reserved.
Focuses on muscles and movement – Maintains muscle tone, posture and balance Fine tunes conscious and unconscious movements directed by the cerebrum Important in learning motor skills – Riding a bike – Taking notes in class Important in proprioception – Knowing where the body is in space © 2013 John Wiley & Sons, Inc. All rights reserved.
A relay center for sensory information and motor responses Centers for visual and auditory startle reflexes are located here The thalamus and hypothalamus are also located here © 2013 John Wiley & Sons, Inc. All rights reserved.
The hypothalamus – Secretes hormones that control the pituitary gland – Also regulates circadian rhythm, body temperature, heart rate, blood pressure and controls smooth muscle contraction The thalamus is a relay station – For incoming sensory information The limbic system – Communicates with the anterior portion of thalamus – Is also responsible for emotions © 2013 John Wiley & Sons, Inc. All rights reserved.
Largest portion of the brain Central processing center where learning, remembering, and activity planning takes place – Information is processed and integrated and appropriate responses are generated Organized into four lobes – Frontal, parietal, occipital, temporal The surface of the cerebrum – Covered in creases (sulci) and raised areas (gyri) © 2013 John Wiley & Sons, Inc. All rights reserved.
The outer layer of cerebrum, called the cerebral cortex, is composed of gray matter – Folded to provide larger surface area – Contains neuronal cell bodies, dendrites, and non- myelinated axons – Responsible for sensations, voluntary movements, and thoughts The inner layer of the cerebrum consists of white matter that is composed of myelinated axons – Myelinated axons are covered in lipids which allows for faster impulse transmission – Information passed between areas of the brain via tracts of white matter © 2013 John Wiley & Sons, Inc. All rights reserved.
The left and right cerebral hemispheres are distinct – The right analyzes sensory input, recognizes faces, and functions in spatial relationships – The left includes general language interpretation and speech, controls writing and speaking, categorizes items and makes logical decisions The cortex has motor areas, sensory areas, and association areas that integrate new information with stored information – The primary motor area formulates voluntary motor commands © 2013 John Wiley & Sons, Inc. All rights reserved.
Association areas of the cerebral cortex integrate and coordinate information The right and left sides of the brain connect through the transverse tracts of the corpus collosum Special senses are integrated in specific areas of the cerebral cortex – Visual interpretation occurs in the occipital lobe – Auditory interpretation occurs in the temporal lobe – Taste interpretation occurs in the parietal lobes © 2013 John Wiley & Sons, Inc. All rights reserved.
Learning does not exist in a vacuum – The brain’s ability to learn is related to what else is going on – Fight or flight conditions drastically reduce the ability to learn Learning is a type of memory – Both play a critical role at both ends of life Memory occurs in three phases – Immediate memory – Short-term memory – Long-term memory © 2013 John Wiley & Sons, Inc. All rights reserved.
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