Figure 12.23a

1
(No Transcript)
2
Thalamus
Basal forebrain
Touch
Prefrontal cortex
Hearing
Smell
Taste
Vision
Hippocampus
Sensory input
Thalamus
(a) Declarativememory circuits
Prefrontal cortex
Association cortex
Medial temporal lobe (hippocampus, etc.)
ACh
ACh
Basal forebrain
Figure 12.23a
3
Brain Structures Involved in Nondeclarative Memory

• Procedural memory
• Basal nuclei relay sensory and motor inputs to
  the thalamus and premotor cortex
• Dopamine from substantia nigra is necessary
• Motor memorycerebellum
• Emotional memoryamygdala

4
Sensory and motor inputs
Premotor cortex
Basal nuclei
Association cortex
Thalamus
Dopamine
Premotor cortex
Substantia nigra
Basal nuclei
Thalamus
Substantia nigra
(b) Procedural (skills) memory circuits
Figure 12.23b
5
Molecular Basis of Memory

• During learning
• Altered mRNA is synthesized and moved to axons
  and dendrites
• Dendritic spines change shape
• Extracellular proteins are deposited at synapses
  involved in LTM
• Number and size of presynaptic terminals may
  increase
• More neurotransmitter is released by presynaptic
  neurons

6
Molecular Basis of Memory

• Increase in synaptic strength (long-term
  potentiation, or LTP) is crucial
• Neurotransmitter (glutamate) binds to NMDA
  receptors, opening calcium channels in
  postsynaptic terminal

7
Molecular Basis of Memory

• Calcium influx triggers enzymes that modify
  proteins of the postsynaptic terminal and
  presynaptic terminal (via release of retrograde
  messengers)
• Enzymes trigger postsynaptic gene activation for
  synthesis of synaptic proteins, in presence of
  CREB (cAMP response-element binding protein) and
  BDNF (brain-derived neurotrophic factor)

8
Protection of the Brain

• Bone (skull)
• Membranes (meninges)
• Watery cushion (cerebrospinal fluid)
• Blood-brain barrier

9
Meninges

• Cover and protect the CNS
• Protect blood vessels and enclose venous sinuses
• Contain cerebrospinal fluid (CSF)
• Form partitions in the skull

10
Meninges

• Three layers
• Dura mater
• Arachnoid mater
• Pia mater

11
Skin of scalp
Periosteum
Bone of skull
Dura mater
Periosteal
Meningeal
Superior sagittal sinus
Arachnoid mater
Pia mater
Arachnoid villus
Subdural space
Blood vessel
Falx cerebri (in longitudinal fissure only)
Subarachnoid space
Figure 12.24
12
Dura Mater

• Strongest meninx
• Two layers of fibrous connective tissue (around
  the brain) separate to form dural sinuses

13
Dura Mater

• Dural septa limit excessive movement of the brain
• Falx cerebriin the longitudinal fissure
  attached to crista galli
• Falx cerebellialong the vermis of the cerebellum
• Tentorium cerebellihorizontal dural fold over
  cerebellum and in the transverse fissure

14
Arachnoid Mater

• Middle layer with weblike extensions
• Separated from the dura mater by the subdural
  space
• Subarachnoid space contains CSF and blood vessels
• Arachnoid villi protrude into the superior
  sagittal sinus and permit CSF reabsorption

15
Skin of scalp
Periosteum
Bone of skull
Dura mater
Periosteal
Meningeal
Superior sagittal sinus
Arachnoid mater
Pia mater
Arachnoid villus
Subdural space
Blood vessel
Falx cerebri (in longitudinal fissure only)
Subarachnoid space
Figure 12.24
16
Pia Mater

• Layer of delicate vascularized connective tissue
  that clings tightly to the brain

17
Cerebrospinal Fluid (CSF)

• Composition
• Watery solution
• Less protein and different ion concentrations
  than plasma
• Constant volume

18
Cerebrospinal Fluid (CSF)

• Functions
• Gives buoyancy to the CNS organs
• Protects the CNS from blows and other trauma
• Nourishes the brain and carries chemical signals

19
Superior sagittal sinus
4
Choroid plexus
Arachnoid villus
Interventricular foramen
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
1
Right lateral ventricle (deep to cut)
Choroid plexus of fourth ventricle
3
Third ventricle
1
CSF is produced by the choroid plexus of
each ventricle.
Cerebral aqueduct
Lateral aperture
2
CSF flows through the ventricles and into
the subarachnoid space via the median and
lateral apertures. Some CSF flows through the
central canal of the spinal cord.
Fourth ventricle
Median aperture
2
Central canal of spinal cord
CSF flows through the subarachnoid space.
3
(a) CSF circulation
4
CSF is absorbed into the dural
venous sinuses via the arachnoid villi.
Figure 12.26a
20
Choroid Plexuses

• Produce CSF at a constant rate
• Hang from the roof of each ventricle
• Clusters of capillaries enclosed by pia mater and
  a layer of ependymal cells
• Ependymal cells use ion pumps to control the
  composition of the CSF and help cleanse CSF by
  removing wastes

21
Blood-Brain Barrier

• Helps maintain a stable environment for the brain
  
• Separates neurons from some bloodborne substances

22
Blood-Brain Barrier

• Composition
• Continuous endothelium of capillary walls
• Basal lamina
• Feet of astrocytes
• Provide signal to endothelium for the formation
  of tight junctions

23
Capillary
Neuron
Astrocyte
(a) Astrocytes are the most abundantCNS
neuroglia.
Figure 11.3a
24
Blood-Brain Barrier Functions

• Selective barrier
• Allows nutrients to move by facilitated diffusion
• Allows any fat-soluble substances to pass,
  including alcohol, nicotine, and anesthetics
• Absent in some areas, e.g., vomiting center and
  the hypothalamus, where it is necessary to
  monitor the chemical composition of the blood

25
Spinal Cord

• Location
• Begins at the foramen magnum
• Ends as conus medullaris at L1 vertebra
• Functions
• Provides two-way communication to and from the
  brain
• Contains spinal reflex centers

26
Spinal Cord Protection

• Bone, meninges, and CSF
• Cushion of fat and a network of veins in the
  epidural space between the vertebrae and spinal
  dura mater
• CSF in subarachnoid space

27
Spinal Cord Protection

• Denticulate ligaments extensions of pia mater
  that secure cord to dura mater
• Filum terminale fibrous extension from conus
  medullaris anchors the spinal cord to the coccyx

28
T12
Ligamentum flavum
L5
Lumbar puncture needle entering subarachnoid space
L4
Supra- spinous ligament
Filum terminale
L5
S1
Inter- vertebral disc
Cauda equina in subarachnoid space
Dura mater
Arachnoid matter
Figure 12.30
29
Cervical spinal nerves
Cervical enlargement
Dura and arachnoid mater
Thoracic spinal nerves
Lumbar enlargement
Conus medullaris
Lumbar spinal nerves
Cauda equina
Filum terminale
Sacral spinal nerves
(a) The spinal cord and its nerve roots,
with the bony vertebral arches removed. The
dura mater and arachnoid mater are cut
open and reflected laterally.
Figure 12.29a
30
Spinal Cord

• Spinal nerves
• 31 pairs
• Cervical and lumbar enlargements
• The nerves serving the upper and lower limbs
  emerge here
• Cauda equina
• The collection of nerve roots at the inferior end
  of the vertebral canal

31
Cross-Sectional Anatomy

• Two lengthwise grooves divide cord into right and
  left halves
• Ventral (anterior) median fissure
• Dorsal (posterior) median sulcus
• Gray commissureconnects masses of gray matter
  encloses central canal

32
Pia mater
Epidural space (contains fat)
Arachnoid mater
Spinal meninges
Subdural space
Dura mater
Subarachnoid space (contains CSF)
Bone of vertebra
Dorsal root ganglion
Body of vertebra
(a) Cross section of spinal cord and vertebra
Figure 12.31a
33
Dorsal median sulcus
Gray commissure
Dorsal funiculus
Dorsal horn
Gray matter
White columns
Ventral funiculus
Ventral horn
Lateral funiculus
Lateral horn
Dorsal root ganglion
Spinal nerve
Central canal
Dorsal root (fans out into dorsal rootlets)
Ventral median fissure
Ventral root (derived from several ventral
rootlets)
Pia mater
Arachnoid mater
Spinal dura mater
(b) The spinal cord and its meningeal coverings
Figure 12.31b
34
Gray Matter

• Dorsal hornsinterneurons that receive somatic
  and visceral sensory input
• Ventral hornssomatic motor neurons whose axons
  exit the cord via ventral roots
• Lateral horns (only in thoracic and lumbar
  regions) sympathetic neurons
• Dorsal root (spinal) gangiacontain cell bodies
  of sensory neurons

35
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic sensory neuron
Visceral sensory neuron
Visceral motor neuron
Spinal nerve
Ventral horn (motor neurons)
Ventral root (motor)
Somatic motor neuron
Interneurons receiving input from somatic sensory
neurons
Interneurons receiving input from visceral
sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Figure 12.32
36
White Matter

• Consists mostly of ascending (sensory) and
  descending (motor) tracts
• Transverse tracts (commissural fibers) cross from
  one side to the other
• Tracts are located in three white columns
  (funiculi on each sidedorsal (posterior),
  lateral, and ventral (anterior)
• Each spinal tract is composed of axons with
  similar functions

37
Pathway Generalizations

• Pathways decussate (cross over)
• Most consist of two or three neurons (a relay)
• Most exhibit somatotopy (precise spatial
  relationships)
• Pathways are paired symmetrically (one on each
  side of the spinal cord or brain)

38
Ascending tracts
Descending tracts
Ventral white commissure
Fasciculus gracilis
Dorsal white column
Fasciculus cuneatus
Lateral reticulospinal tract
Dorsal spinocerebellar tract
Lateral corticospinal tract
Rubrospinal tract
Ventral spinocerebellar tract
Medial reticulospinal tract
Lateral spinothalamic tract
Ventral corticospinal tract
Ventral spinothalamic tract
Vestibulospinal tract
Tectospinal tract
Figure 12.33
39
Ascending Pathways

• Consist of three neurons
• First-order neuron
• Conducts impulses from cutaneous receptors and
  proprioceptors
• Branches diffusely as it enters the spinal cord
  or medulla
• Synapses with second-order neuron

40
Ascending Pathways

• Second-order neuron
• Interneuron
• Cell body in dorsal horn of spinal cord or
  medullary nuclei
• Axons extend to thalamus or cerebellum

41
Ascending Pathways

• Third-order neuron
• Interneuron
• Cell body in thalamus
• Axon extends to somatosensory cortex

42
Ascending Pathways

• Two pathways transmit somatosensory information
  to the sensory cortex via the thalamus
• Dorsal column-medial lemniscal pathways
• Spinothalamic pathways
• Spinocerebellar tracts terminate in the
  cerebellum

43
Descending Pathways and Tracts

• Deliver efferent impulses from the brain to the
  spinal cord
• Direct pathwayspyramidal tracts
• Indirect pathwaysall others

44
Descending Pathways and Tracts

• Involve two neurons
• Upper motor neurons
• Pyramidal cells in primary motor cortex
• Lower motor neurons
• Ventral horn motor neurons
• Innervate skeletal muscles

45
The Direct (Pyramidal) System

• Impulses from pyramidal neurons in the precentral
  gyri pass through the pyramidal (corticospinal)l
  tracts
• Axons synapse with interneurons or ventral horn
  motor neurons
• The direct pathway regulates fast and fine
  (skilled) movements

46
Indirect (Extrapyramidal) System

• Includes the brain stem motor nuclei, and all
  motor pathways except pyramidal pathways
• Also called the multineuronal pathways

47
Indirect (Extrapyramidal) System

• These pathways are complex and multisynaptic, and
  regulate
• Axial muscles that maintain balance and posture
• Muscles controlling coarse movements
• Head, neck, and eye movements that follow objects

48
Indirect (Extrapyramidal) System

• Reticulospinal and vestibulospinal
  tractsmaintain balance
• Rubrospinal tractscontrol flexor muscles
• Superior colliculi and tectospinal tracts mediate
  head movements in response to visual stimuli