Support, Movement, Senses The Brain - Mission...

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Support, Movement, Senses… The Brain…

References- chapters 48, 49


Nervous systems consist of circuits of neurons and supporting cells

§  By the Cambrian explosion, specialized systems of neurons enabled animals to sense and respond to their environments

§  The simplest nervous systems (in cnidarians) have neurons arranged in nerve nets- a series of interconnected nerve cells

§  More complex animals have nerves, in which axons of multiple neurons are bundled together


Figure 49.2

Nerve net

Radial nerve Nerve ring

Eyespot

Brain Nerve cords Transverse nerve

Brain

Ventral nerve cord

Segmental ganglia

Brain Ventral nerve cord

Segmental ganglia

Anterior nerve ring

Longitudinal nerve cords

Ganglia

Brain

Ganglia

Brain

Spinal cord (dorsal nerve cord)

Sensory ganglia

(a) Hydra (cnidarian) (b) Sea star (echinoderm) (c) Planarian (flatworm) (d) Leech (annelid)

(e) Insect (arthropod) (f) Chiton (mollusc) (g) Squid (mollusc) (h) Salamander (vertebrate)


§  Bilaterally symmetrical animals exhibit cephalization, clustering of sensory organs at the front end of body

§  The simplest cephalized animals, flatworms, have a central nervous system (CNS)- consisting of a brain and longitudinal nerve cords

§  The peripheral nervous system (PNS) consists of neurons carrying information into and out of the CNS


Figure 49.6

Central nervous system (CNS)

Brain

Spinal cord

Cranial nerves

Ganglia outside CNS

Spinal nerves

Peripheral nervous system (PNS)


§  Nervous system organization correlates with lifestyle

§  Sessile molluscs (for example, clams and chitons) have simple systems, whereas more complex molluscs (for example, octopuses and squids) have more sophisticated systems


§  The spinal cord conveys information to and from the brain and generates basic patterns of locomotion

§  Spinal cord also produces reflexes independently of the brain

§  A reflex is the body’s automatic response to a stimulus

§  Ex: mallet triggers a knee-jerk reflex

The Central Nervous System


Figure 49.7

Quadriceps muscle

Hamstring muscle

Key Sensory neuron Motor neuron Interneuron

Cell body of sensory neuron in dorsal root ganglion Gray

matter White matter

Spinal cord (cross section)


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


§  The PNS has two efferent components: the motor system and the autonomic nervous system

§  Motor system carries signals to skeletal muscles and is voluntary

§  Autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary


§  The autonomic nervous system has sympathetic and parasympathetic divisions

§  Sympathetic division regulates arousal and energy generation (“fight-or-flight” response)

§  Parasympathetic division has antagonistic effects on target organs and promotes calming and a return to “rest and digest” functions


Figure 49.9

Parasympathetic division Sympathetic division

Constricts pupil of eye Dilates pupil of eye

Stimulates salivary gland secretion

Inhibits salivary gland secretion

Relaxes bronchi in lungs Constricts bronchi in lungs

Slows heart Accelerates heart

Inhibits activity of stomach and intestines

Inhibits activity of pancreas

Stimulates activity of stomach and intestines

Stimulates activity of pancreas

Stimulates gallbladder

Promotes emptying of bladder

Promotes erection of genitalia

Stimulates glucose release from liver; inhibits gallbladder

Stimulates adrenal medulla

Inhibits emptying of bladder

Promotes ejaculation and vaginal contractions

Sympathetic ganglia Cervical

Thoracic

Lumbar

Sacral

Synapse


The vertebrate brain is regionally specialized

§  Brain structures are specialized for diverse functions

§  Forebrain has activities including processing olfactory input, regulating sleep, learning

§  Midbrain coordinates routing of sensory input

§  Hindbrain controls involuntary activities, coordinates motor activities


§  Comparison of vertebrates shows that relative sizes of particular brain regions vary

§  These size differences reflect the relative importance of the particular brain function

§  Evolution has resulted in a close match between structure and function

Lamprey

Shark

Ray-finned fish Amphibian

Crocodilian

Bird

Mammal

ANCESTRAL VERTEBRATE

Key Forebrain Midbrain Hindbrain


Figure 49.11b

Embryonic brain regions Brain structures in child and adult

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon Medulla oblongata (part of brainstem)

Pons (part of brainstem), cerebellum

Midbrain (part of brainstem)

Diencephalon (thalamus, hypothalamus, epithalamus)

Cerebrum (includes cerebral cortex, basal nuclei)

Cerebrum Diencephalon Mesencephalon Metencephalon

Myelencephalon Diencephalon

Telencephalon Spinal cord

Child Embryo at 5 weeks Embryo at 1 month

Forebrain

Midbrain

Hindbrain

Hindbrain

Midbrain Pons Medulla oblongata Cerebellum Spinal cord

Brainstem

Midbrain

Forebrain


Arousal and Sleep

§  The brainstem and cerebrum control arousal and sleep; sleep also regulated by biological clock

§  Sleep is essential for learning and memory

§  Some animals have evolutionary adaptations allowing substantial activity during sleep

§  Dolphins sleep with one brain hemisphere at a time and are therefore able to swim while “asleep”


Biological Clock Regulation

§  Cycles of sleep and wakefulness are examples of circadian rhythms, daily cycles of biological activity

§  Such rhythms rely on a biological clock, a molecular mechanism that directs periodic gene expression and cellular activity

§  Biological clocks are typically synchronized to light and dark cycles


Emotions

§  Generation and experience of emotions involve many brain structures- the amygdala, hippocampus, thalamus- grouped as the limbic system

Thalamus

Hypothalamus

Olfactory bulb

Amygdala Hippocampus


The cerebral cortex controls voluntary movement and cognitive functions

§  The cerebrum, the largest structure in the human brain, is essential for language, cognition, memory, consciousness, and awareness of our surroundings

Skeletal muscle control Sense of touch Integration of sensory information

Frontal lobe

Temporal lobe

Parietal lobe

Occipital lobe

Decision making, planning

Forming speech

Hearing Cerebellum

Combining images and object recognition

Processing visual stimuli, pattern recognition Language comprehension


Figure 49.18

Hearing words

Seeing words

Max

Min

Generating words

Speaking words


Lateralization of Function

§  The two hemispheres make distinct contributions to brain function

§  Left hemisphere more adept at language, math, logic

§  Right hemisphere stronger at facial and pattern recognition, spatial relations, nonverbal thinking

§  The two hemispheres work together by communicating through fibers of the corpus callosum


Many nervous system disorders can be explained in molecular terms

§  Disorders of the nervous system include schizophrenia, depression, drug addiction, Alzheimer’s disease, Parkinson’s disease

§  Genetic and environmental factors contribute to diseases of the nervous system


The Brain’s Reward System and Drug Addiction

§  Some drugs are addictive because they increase activity of the brain’s dopamine reward (“pleasure”) system

§  Cocaine, amphetamine, heroin, alcohol, and tobacco

§  Drug addiction is characterized by compulsive consumption and an inability to control intake

§  Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug


Alzheimer’s Disease

§  Mental deterioration characterized by confusion and memory loss- caused by formation of neurofibrillary tangles and amyloid plaques in the brain

§  No cure for this disease- some drugs relieve symptoms

Amyloid plaque Neurofibrillary tangle 20 µm


Parkinson’s Disease

§  A motor disorder caused by death of dopamine-secreting neurons in the midbrain

§  Characterized by muscle tremors, flexed posture, and a shuffling gait

§  No cure, although drugs and various other approaches may manage symptoms


Senses

§  The star-nosed mole can catch insect prey in near total darkness in as little as 120 milliseconds

§  Uses 11 pairs of appendages protruding from its nose to locate and capture prey

§  Sensory processes convey information about an animal’s environment to its brain; muscles carry out movements as instructed by the brain


Sensory receptors transduce stimulus energy and transmit signals to the CNS

§  All stimuli represent forms of energy

§  When a stimulus’s input to the nervous system is processed, a motor response may be generated

§  May involve a simple reflex or elaborate processing

Mole forages along tunnel

Food absent

Mole moves on

Mole bites Food present

OR

Sensory input Integration Motor output


§  Sensory pathways have four basic functions in common:

§  Sensory reception- detection of stimuli by sensory receptors

§  Transduction- conversion of stimulus energy; magnitude varies with stimuli intensity

§  Transmission- to the CNS

§  Integration- brain distinguishes stimuli from different receptors based on where they arrive in the brain


Types of Sensory Receptors

§  Based on energy transduced, sensory receptors fall into five categories

§  Mechanoreceptors

§  Chemoreceptors

§  Electromagnetic receptors

§  Thermoreceptors

§  Pain receptors


Hearing and Equilibrium in Mammals

§  In most terrestrial vertebrates, sensory organs for hearing and equilibrium are closely associated in the ear

§  For both senses, settling particles or moving fluid is detected by mechanoreceptors

Ciliated receptor cells

Cilia

Statolith

Sensory nerve fibers (axons)

The statocyst is used to sense equilibrium


Hearing

§  Vibrating objects create percussion waves in air, causing tympanic membrane vibration

§  The three bones of the middle ear transmit vibrations of moving air to the cochlea

§  Vibrations create pressure waves in fluid in the cochlea that travel through the vestibular canal Tympanic

membrane

Cochlea

Sensory neurons


§  The ear conveys information about

§  Volume- the amplitude of the sound wave

§  Pitch- the frequency of the sound wave

Hearing


Hearing and Equilibrium in Other Vertebrates

§  Unlike mammals, fishes have only inner ears (near the brain)

§  Fishes also have a lateral line system that contains mechanoreceptors with hair cells to detect water movement

Side view

Top view

Lateral line

Cross section

Supporting cell Nerve fiber Action potentials

Nerve Lateral nerve FISH BODY WALL

Scale Segmental muscle

Water flow

Cupula

Sensory hairs Hair cell

Lateral line epidermis

Lateral line canal Water flow

Opening of lateral line canal

SURROUNDING WATER


Diverse visual receptors of animals depend on light-absorbing pigments

§  Animals use diverse organs for vision, but the underlying mechanism for capturing light is the same, suggesting a common evolutionary origin

§  Light detectors range from simple clusters of cells that detect direction and intensity of light, to complex organs that form images

§  Light detectors all contain photoreceptors, cells that contain light-absorbing pigment molecules


Light-Detecting Organs

§  Most invertebrates have a light-detecting organ

§  One of the simplest light-detecting organs is that of planarians

§  A pair of ocelli called eyespots are located near the head

§  These allow planarians to move away from light and seek shaded locations


Compound Eyes

§  Insects and crustaceans have compound eyes, which consist of up to several thousand light detectors called ommatidia

§  Compound eyes are effective at detecting movement

§  Insects have excellent color vision, and some can see into the ultraviolet range


Single-Lens Eyes

§  Among invertebrates, single-lens eyes are found in some jellies, polychaetes, spiders, and molluscs

§  Work like a camera- iris changes the pupil diameter to control how much light enters

§  Eyes of all vertebrates have a single lens- eye detects color and light, but brain assembles information and perceives an image


Figure 50.17a

Sclera Choroid Retina

Fovea

Optic nerve

Central artery and vein of the retina

Optic disk

Vitreous humor

Lens

Aqueous humor

Pupil

Iris

Cornea

Suspensory ligament

Optic nerve fibers

Ganglion cell

Bipolar cell

Horizontal cell

Amacrine cell Pigmented

epithelium

Retina

Neurons Rod Cone

Photoreceptors


Color Vision

§  Among vertebrates, most fish, amphibians, and reptiles, including birds, have good color vision

§  In humans, perception of color is based on three types of cones (photoreceptors), each with a different visual pigment: red, green, or blue

§  Mammals that are nocturnal usually have a high proportion of rods (photoreceptors that differentiate objects in low light) in the retina


§  Abnormal color vision results from alterations in the genes for one or more photopsin proteins

§  In 2009, researchers studying color blindness in squirrel monkeys made a breakthrough in gene therapy


The senses of taste and smell rely on similar sets of sensory receptors

§  In terrestrial animals,

§  Gustation (taste) is dependent on the detection of chemicals called tastants; In mammals, there are five taste perceptions: sweet, sour, salty, bitter, umami

§  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 located on feet and in mouth parts


The physical interaction of protein filaments is required for muscle function

§  Muscle activity is a response to input from the nervous system

§  Vertebrate skeletal muscle moves bones and the body

§  Glycolysis and aerobic respiration generate the energy (ATP) needed to sustain muscle contraction

Muscle

Nuclei

Bundle of muscle fibers

Single muscle fiber (cell)

Plasma membrane

Myofibril


§  Amyotrophic lateral sclerosis (ALS), formerly called Lou Gehrig’s disease, interferes with the excitation of skeletal muscle fibers; this disease is usually fatal


Nervous Control of Muscle Tension

§  Contraction of a whole muscle is graded, which means that the extent and strength of its contraction can be voluntarily altered

§  There are two basic mechanisms by which the nervous system produces graded contractions

§  Varying the number of fibers that contract

§  Varying the rate at which fibers are stimulated


Figure 50.31 Spinal cord

Motor neuron cell body

Motor unit 1

Motor unit 2

Nerve

Motor neuron axon

Muscle Muscle fibers

Tendon

Synaptic terminals


Other Types of Muscle

§  In addition to skeletal muscle, vertebrates have cardiac muscle and smooth muscle

§  Cardiac muscle, found only in the heart, consists of striated cells electrically connected by intercalated disks

§  Smooth muscle is found mainly in walls of hollow organs such as those of the digestive tract

§ Contractions are relatively slow and may be initiated by the muscles themselves

§ Contractions may also be caused by stimulation from neurons in the autonomic nervous system


Skeletal systems transform muscle contraction into locomotion

§  The skeleton provides a rigid structure to which muscles attach

§  Skeletons function in support, protection, and movement

Biceps

Triceps

Flex

ion

Human forearm (internal skeleton)

Grasshopper tibia (external skeleton)

Extensor muscle

Flexor muscle

Extensor muscle

Flexor muscle

Ext

ensi

on

Biceps

Triceps

Relaxing muscle Contracting muscle Key


Types of Skeletal Systems

§  The three main types of skeletons are

§  Hydrostatic skeletons (lack hard parts)

§  Exoskeletons (external hard parts)

§  Endoskeletons (internal hard parts)


§  The skeletons of small and large animals have different proportions, underlying function

§  In mammals and birds, the position of legs relative to the body is very important in determining how much weight the legs can bear


Types of Locomotion

§  Most animals are capable of locomotion- active travel from place to place

§  In locomotion, energy is expended to overcome friction and gravity


Locomotion on Land

§  Walking, running, hopping, or crawling on land requires an animal to support itself and move against gravity

§  Diverse adaptations for locomotion on land have evolved in vertebrates


§  Air poses relatively little resistance for land locomotion

§  Maintaining balance is a prerequisite to walking, running, or hopping

§  Crawling poses a different challenge; a crawling animal must exert more energy to overcome friction


Swimming

§  In water, friction is a bigger problem than gravity

§  Fast swimmers usually have a sleek, torpedo-like shape to minimize friction

§  Animals swim in diverse ways

§  Paddling with their legs as oars

§  Jet propulsion

§  Undulating their body and tail from side to side, or up and down


Flying

§  Active flight requires that wings develop enough lift to overcome the downward force of gravity

§  Many flying animals have adaptations that reduce body mass

§  Ex: birds have no urinary bladder or teeth, and have relatively large bones with air-filled regions


Figure 50.UN01a

Flying Running

Swimming

Body mass (g) (log scale) 10-3 1 103 106

1

10

102

10-1

Ener

gy c

ost (

cal/k

g ・ m

) (lo

g sc

ale)

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