Chapter 49 Nervous Systems PDF

Chapter 49 Nervous Systems Dr Salamah Alwahsh 2024 PowerPoint® Lecture Presentations for Biology Eighth E...

Chapter 49 Nervous Systems Dr Salamah Alwahsh 2024 PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  In vertebrates – The CNS is composed of the brain and spinal cord. – The peripheral nervous system (PNS) is composed of nerves and ganglia. Nerves are bundles that consist of the axons of multiple nerve cells. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Organization of the Vertebrate Nervous System The spinal cord conveys information from the brain to the PNS. The spinal cord also produces reflexes independently of the brain. A reflex is the body’s automatic response to a stimulus – For example, a doctor uses a mallet to trigger a knee-jerk reflex. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings knee- jerk Cell body of Gray sensory neuron in matter Reflex Quadriceps dorsal root muscle ganglion White matter Hamstring muscle Spinal cord (cross section) Sensory neuron Motor neuron Interneuron Vertebrate Central nervous Peripheral nervous Nervous system (CNS) system (PNS) System Brain Cranial Vertebrates Spinal nerves have dorsal cord spinal cord Ganglia outside CNS Spinal nerves The spinal cord and brain develop from the embryonic nerve cord. Ventricles, gray matter, and white matter Gray matter White matter Ventricles  The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  The brain and spinal cord contain – Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons. – White matter, which consists of bundles of myelinated axons. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Peripheral Nervous System The PNS transmits information to and from the CNS and regulates movement and the internal environment. In the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNS. Cranial nerves originate in the brain and mostly terminate in organs of the head and upper body. Spinal nerves originate in the spinal cord and extend to parts of the body below the head. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings peripheral nervous system PNS Efferent Afferent neurons (sensory) neurons Motor Autonomic system nervous system Hearing Sympathetic Parasympathetic Enteric Locomotion division division division Hormone Gas exchange Circulation action Digestion  The PNS has two functional components: the motor system and the autonomic nervous system. The motor system carries signals to skeletal muscles and is voluntary. The autonomic nervous system regulates the internal environment in an involuntary manner ANS has sympathetic, parasympathetic, and enteric divisions The sympathetic and parasympathetic divisions have antagonistic effects on target organs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  The sympathetic division correlates with the “fight-or-flight” response. The parasympathetic division promotes a return to “rest and digest” The enteric division controls activity of the digestive tract, pancreas, and gallbladder. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PNS: Parasympathetic division Sympathetic division autonomic nervous Action on target organs: Action on target organs: system Constricts pupil Dilates pupil of eye of eye Stimulates salivary Inhibits salivary gland secretion gland secretion Sympathetic Constricts ganglia Relaxes bronchi bronchi in lungs Cervical in lungs Slows heart Accelerates heart Stimulates activity Inhibits activity of stomach and of stomach and intestines intestines Thoracic Stimulates activity Inhibits activity of pancreas of pancreas Stimulates Stimulates glucose gallbladder release from liver; inhibits gallbladder Lumbar Stimulates adrenal medulla Promotes emptying Inhibits emptying of bladder of bladder Promotes erection Sacral Promotes ejaculation and of genitals Synapse vaginal contractions  Brainstem The midbrain contains centers for receipt and integration of sensory information. The pons regulates breathing centers in the medulla. The medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Cerebellum The cerebellum is important for coordination and error checking during motor, perceptual, and cognitive functions It is also involved in learning and remembering motor skills Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Diencephalon The diencephalon develops into three regions: the epithalamus, thalamus, and hypothalamus. The epithalamus includes the pineal gland and generates cerebrospinal fluid from blood. The thalamus is the main input center for sensory information to the cerebrum and the main output center for motor information leaving the cerebrum. The hypothalamus regulates homeostasis and basic survival behaviors such as feeding, fighting, fleeing, and reproducing. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cerebrum  Cerebrum The cerebrum has right and left cerebral hemispheres. Each cerebral hemisphere consists of a cerebral cortex (gray matter) overlying white matter and basal nuclei. In humans, the cerebral cortex is the largest and most complex part of the brain. The basal nuclei are important centers for planning and learning movement sequences. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  A thick band of axons called the corpus callosum provides communication between the right and left cerebral cortices. The right half of the cerebral cortex controls the left side of the body, and vice versa. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Human Brain viewed from the rear Left cerebral Right cerebral hemisphere hemisphere Corpus Thalamus callosum Basal Cerebral nuclei cortex  human cerebral cortex Frontal lobe Parietal lobe Somatosensory Speech association Frontal association area area Taste Reading Speech Hearing Visual Smell association Auditory association area area Vision Temporal lobe Occipital lobe Nervous system disorders can be explained in molecular terms Disorders of the nervous system include schizophrenia, depression, Alzheimer’s disease, and Parkinson’s disease. Genetic and environmental factors contribute to diseases of the nervous system. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Drug Addiction and the Brain Reward System The brain’s reward system rewards motivation with pleasure. Some drugs are addictive because they increase activity of the brain’s reward system. These drugs include cocaine, amphetamine, heroin, alcohol, and tobacco. Drug addiction is characterized by compulsive consumption and an inability to control intake. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Addictive drugs enhance the activity of the dopamine pathway. Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Effects of addictive drugs on the reward pathway of the mammalian brain Nicotine stimulates dopamine- releasing VTA neuron. Opium and heroin decrease activity of inhibitory neuron. Cocaine and amphetamines block removal of dopamine. Cerebral neuron of Reward reward system pathway response Alzheimer’s Disease Alzheimer’s disease is a mental deterioration characterized by confusion, memory loss, and other symptoms. Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brain. A successful treatment in humans may hinge on early detection of amyloid plaques. There is no cure for this disease though some drugs are effective at relieving symptoms. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Microscopic signs of Alzheimer’s disease Amyloid plaque Neurofibrillary tangle 20 µm Stem Cell–Based Therapy Unlike the PNS, the CNS cannot fully repair itself. However, it was recently discovered that the adult human brain contains stem cells that can differentiate into mature neurons. Induction of stem cell differentiation and transplantation of cultured stem cells are potential methods for replacing neurons lost to trauma or disease. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Human Brain Cerebral cortex Cerebrum Forebrain Thalamus Hypothalamus Pituitary gland Midbrain Pons Spinal Hindbrain Medulla cord oblongata Cerebellum Special sensation ‫الحواس‬  Types of Sensory Receptors Based on energy transduced, sensory receptors fall into five categories: – Mechanoreceptors: sense physical deformation caused by stimuli such as pressure, stretch, motion, and sound – Chemoreceptors: transmit information about the total solute concentration of a solution – Electromagnetic receptors (e.g., photoreceptors) detect light, electricity, and magnetism – Thermoreceptors – Pain receptors Sensory Heat Gentle Pain Cold Hair receptors in touch human skin Epidermis Dermis Hypodermis Nerve Connective Hair Strong tissue movement pressure  Specialized electromagnetic receptors Eye Infrared receptor (a) Rattlesnake – infrared receptors detect body heat of prey ‫الضحية‬ (b) Beluga whales sense Earth’s magnetic field – as they navigate migrations.  Thermoreceptors & Pain Receptors Thermoreceptors, which respond to heat or cold, help regulate body temperature by signaling both surface and body core temperature. In humans, pain receptors, or nociceptors, are a class of naked dendrites in the epidermis. They respond to excess heat, pressure, or chemicals released from damaged or inflamed tissues. The mechanoreceptors responsible for hearing and equilibrium detect moving fluid or settling particles Hearing and perception of body equilibrium are related in most animals. Settling particles or moving fluid are detected by mechanoreceptors. Human Ear Middle In most vertebrates, sensory organs Outer ear ear Inner ear for hearing and equilibrium are Skull Stapes ‫الركاب‬ closely associated in the ear bone ‫سندان‬ Incus Semicircular canals Malleus Auditory nerve Cochlear Bone Auditory ‫مطرقة‬ to brain duct nerve Vestibular canal ‫القوقعة‬ Tympanic Cochlea canal Oval window Eustachian Pinna Auditory tube canal Tympanic Round Organ of Corti membrane window ‫غشاء الطبلة‬ Hair cells Tectorial membrane Hair cell bundle from a bullfrog; the longest cilia shown are ~8 µm (SEM). Basilar Axons of To auditory membrane sensory neurons nerve  Hearing Vibrating objects create percussion waves ‫اهتزازات‬ in the air that cause the tympanic membrane to vibrate Hearing is the perception of sound in the brain from the vibration of air waves. The three bones of the middle ear transmit the vibrations of moving air to the oval window on the cochlea. These vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canal. Pressure waves in the canal cause the basilar membrane to vibrate, bending its hair cells. This bending of hair cells depolarizes the membranes of mechanoreceptors and sends action potentials to the brain via the auditory nerve Sensory reception by hair cells. “Hairs” of hair cell Neuro- More trans- neuro- Less mitter at trans- neuro- synapse mitter trans- mitter Sensory –50 –50 Receptor potential –50 neuron potential (mV) potential (mV) potential (mV) –70 –70 –70 Membrane Membrane Membrane Action potentials 0 0 0 Signal Signal Signal –70 –70 –70 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Time (sec) Time (sec) Time (sec) (a) No bending of hairs (b) Bending of hairs in one direction (c) Bending of hairs in other direction The ear conveys information about sound waves: Volume = amplitude of the sound wave Pitch = frequency of the sound wave The cochlea can distinguish pitch because the basilar membrane is not uniform along its length. Each region vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex. Organs of equilibrium in the inner ear Semicircular canals Flow of fluid ‫قُبة‬ Vestibular nerve Cupula Hairs Hair cells Vestibule Axons ‫الدهليز‬ Utricle Body movement Saccule  The senses of taste and smell rely onanimals: In terrestrial similar sets of sensory receptors – Gustation (taste) is dependent on the detection of chemicals called tastants – Olfaction (smell) is dependent on the detection of odorant molecules In aquatic animals there is no distinction between taste and smell. Taste receptors of insects are in sensory hairs called sensilla, located on feet and in mouth parts.  Taste in Mammals In humans, receptor cells for taste are modified epithelial cells organized into taste buds. There are five taste perceptions: sweet, sour, salty, bitter, and umami (elicited by glutamate in meat, cheese, …) Each type of taste can be detected in any region of the tongue. When a taste receptor is stimulated, the signal is transduced to a sensory neuron. Each taste cell has only one type of receptor.  Smell in Humans Olfactory receptor cells are neurons that line the upper portion of the nasal cavity. Binding of odorant molecules to receptors triggers a signal transduction pathway, sending action potentials to the brain. Smell in humans Brain Action potentials Olfactory bulb Odorants Nasal cavity Bone Epithelial cell Odorant receptors Chemo- receptor Plasma Cilia membrane Odorants Mucus  Structure of the Eye Main parts of the vertebrate eye: – The sclera: white outer layer, including cornea – The choroid: pigmented layer (melanin) – The iris: regulates the size of the pupil – The retina: contains photoreceptors – The lens: focuses light on the retina – The optic disk: a blind spot in the retina where the optic nerve attaches to the eye. The eye is divided into two cavities separated by the lens and ciliary body: – The anterior cavity is filled with watery aqueous humor – The posterior cavity is filled with jellylike vitreous humor The ciliary body produces the aqueous humor. Vertebrate Eye Sclera Choroid ‫الشبكية‬ Ciliary body ‫غالف العين المشيمي غشاء العين الخارجي‬ Retina Suspensory Fovea = center ligament of visual field ‫ القرنية‬Cornea Iris Optic ‫العصب‬ ‫البصري‬ nerve Pupil ‫البؤبؤ‬ Aqueous humor Lens ‫العدسة‬ Central artery and vein of the retina Vitreous humor ‫الجسم الزجاجي‬ Optic disk (blind spot) Humans and other mammals focus light by changing the shape of the lens. Ciliary muscles Ciliary muscles relax. contract. Choroid Suspensory Suspensory Retina ligaments pull ligaments relax. against lens. Lens becomes thicker and Lens becomes rounder. flatter. (a) Near vision (accommodation) (b) Distance vision The human retina contains two types of photoreceptors: rods and cones Rods are light-sensitive but don’t distinguish colors. Cones distinguish colors but are not as sensitive to light. In humans, cones are concentrated in the fovea ‫النقرة‬, the center of the visual field, and rods are more concentrated around the periphery of the retina. Sensory Transduction in the Eye Each rod or cone contains visual pigments consisting of a light-absorbing molecule called retinal bonded to a protein called an opsin. Rods contain the pigment rhodopsin (retinal combined with a specific opsin), which changes shape when absorbing light. Once light activates rhodopsin, cyclic GMP breaks down, and Na+ channels close. This hyperpolarizes the cell Receptor potential production in a rod cell Inside of disk EXTRACELLULAR Light FLUID Disk membrane Active rhodopsin Phosphodiesterase Plasma membrane CYTOSOL Sodium channel cGMP Inactive Transducin rhodopsin GMP Na+ Dark 0 potential (mV) Light Membrane –40 Hyper- polarization Na+ –70 Time Processing of Visual Information In humans, three pigments called photopsins detect light of different wave lengths: red, green, or blue. Processing of visual information begins in the retina. Absorption of light by retinal triggers a signal transduction pathway. Neural pathways for vision Right Optic visual chiasm field Right eye Left eye Left visual Optic nerve Lateral Primary field geniculate visual cortex nucleus