Mammalian Nervous System

Structure and Higher Functions

Nervous System Components• CNS - central nervous system

– brain and spinal cord• PNS - peripheral nervous system

– nerves extending to/from CNS• cranial and spinal nerves

–each nerve transmits information to & from the CNS

conceptual organization• afferent information

– coming in to the CNS from the PNS– conscious or unconscious

• efferent information– flowing from the CNS to the PNS– voluntary or involuntary (autonomic)

• hormonal signals – received and sent by CNS

information flow diagramFigure 46.1

Anatomical development• hollow embryonic neural tube

– anterior/posterior extension; dorsal position– three anterior swellings

• prospective hindbrain, midbrain, forebrain– posterior portion becomes spinal cord– cranial & spinal nerves (PNS) sprout from

neural tube

early brain developmentFigure 46.2

Anatomical development

• hindbrain produces

– medulla basic physiological & motor

– pons activities; conduct signals

– cerebellum refinement of motor commands

later development & adult brainFigure 46.2

Anatomical development• midbrain

– basic visual/auditory processing centers– conduct signals

Anatomical development• forebrain produces two parts

– diencephalon: central• thalamus - final relay of information to higher processing areas

• hypothalamus - regulates physiological function, biological drives

Anatomical development• forebrain produces two parts

– telencephalon (cerebrum)• cerebral hemispheres mediate

–sensation–learning–memory–conscious behavior

Anatomical development• brain stem

– medulla, pons, midbrain– conducts, processes information from spinal

cord– primitive & autonomic functions are

controlled lowest on brain stem

Functional subsystems• CNS processes many types of information

simultaneously (parallel processing)– different parts of the CNS handle different

types of information - functional subsystems– parts of different anatomical regions form

the functional subsystems

Functional subsystems

• spinal cord

– conducts information to and from the brain and effectors

– processes some information directly

• spinal reflex

–conversion of afferent to efferent information without brain involvement

the knee jerk reflex

mono- & polysynaptic

pathwaysFigure 46.3

Functional subsystems• spinal cord

– conducts information to and from the brain and effectors• gray matter contains cell bodies• white matter contains axons• each spinal nerve bears

–neural afferents to the dorsal horn–neural efferents from the ventral horn

Functional subsystems• spinal cord

– interneurons • reside in gray matter• connect sensory & motor neurons• participate in spinal processing of reflex and repetitive motor activities

Functional subsystems• reticular system

– through core of medulla, pons & midbrain– complex network of axons & dendrites– distinct nuclei process different types of

information– information also continues to centers of

conscious recognition– reticular activating system regulates

wakefulness/sleep

human limbic systemFigure 46.4

Functional subsystems• limbic system

– primitive structures of telencephalon– regulates basic physiological drives,

emotions, instincts– amygdala mediates fear & fear memory

formation– hippocampus participates in long-term

memory formation

Functional subsystems• cerebrum

– contains many interacting regions– produce consciousness, behavioral control

• cerebral cortex– gray matter - cell bodies

• surface area increased by convolution–ridges = gyri–valleys = sulci–area ~1 m2

• white matter - interconnecting axons

Functional subsystems• Cerebrum

– anatomical organization • each hemisphere includes four lobes

–frontal lobe–parietal lobe–occipital lobe–temporal lobe

anatomical organizationFigure 46.5

Functional subsystems• Cerebrum

– functions• frontal lobe

–primary motor cortex»motor neurons connect with specific muscles

–association areas»contextualization»planning

functional organizationFigure 46.5

Functional subsystems• Cerebrum

– functions• parietal lobe

–primary somatosenory cortex»information from thalamus about touch & pressure sensations

–association areas»attention to complex stimuli»hemispheres are asymmetrical

contralateral neglect syndrome:Figure 46.9

due to right parietal damage

functional organizationFigure 46.7

Functional subsystems• Cerebrum

– functions• occipital lobe

–reception/processing of visual information

• association areas–integrate visual images–convert visual information to language

Functional subsystems• Cerebrum

– functions• temporal lobe

–reception/processing of auditory information

• association areas–object recognition, identification,

naming

face recognition in temporal lobeFigure 46.6

neuronal networks

• autonomic nervous system– controls organs & organ systems– two opposed divisions

• sympathetic division• parasympathetic division

– each division• begins in brain stem or spinal cord• preganglionic neurons use acetylcholine• synapses with ganglia outside the CNS

neuronal networks

• autonomic nervous system– sympathetic division

• preganglionic neurons –emerge below neck–synapse with ganglia near spinal cord

• postganglionic neurons–use norepinephrine as neurotransmitter

sympathetic division of

autonomic nervous system

Figure 46.10

neuronal networks

• autonomic nervous system– parasympathetic division

• preganglionic neurons –emerge from brain stem or base of

spine–synapse with ganglia near target organs

• postganglionic neurons–use acetylcholine as neurotransmitter

parasympathetic division of autonomic nervous system

Figure 46.10

neuronal networks

• autonomic nervous system– organs receiving signals from both divisions

respond oppositely to the two different neurotransmitters

human retinal organizationFigure 45.20

neuronal networks

• regions of the occipital lobe integrate visual information– visual information

• arrives from retinal ganglia through optic nerve

• passes through thalamic relay • arrives at visual cortex of occipital lobe

neuronal networks

• visual information processing– visual cortex cells

• have receptive fields on the retina–simple cells

»localized receptive fields»stimulated by bars of specific orientation

neuronal networks

• visual information processing– visual cortex cells

• have receptive fields on the retina–complex cells

»larger receptive fields»composite of several simple cells with same orientation

»some respond to movement in specific direction

model of cellular

processing of visual signals

Figure 46.11

neuronal networks

• visual information processing– 100,000,000 visual receptors– 2,000,000 retinal ganglion axons– >100,000,000 visual cortex neurons

• each has specific receptive field• each processing circuit functions in parallel

with all others

neuronal networks

• visual information processing-binocular vision– information from left visual field is

processed by right hemisphere– information from right visual field is

processed by left hemisphere– some information from each eye crosses at

the optic chiasm

axons cross at the optic chiasmFigure 46.12

neuronal networks

• visual information processing-binocular vision– one location on visual cortex receives

information from both eyes about the same spot in the visual field• columns of cells receive left or right eye inputs

• cells in each column receive both• binocular cells interpret distance from the disparity between the two retinas

binocular interpretation of visual informationFigure 46.12